[SPARK-3359][DOCS] Make javadoc8 working for unidoc/genjavadoc compatibility in Java API documentation

## What changes were proposed in this pull request?

This PR make `sbt unidoc` complete with Java 8.

This PR roughly includes several fixes as below:

- Fix unrecognisable class and method links in javadoc by changing it from `[[..]]` to `` `...` ``

  ```diff
  - * A column that will be computed based on the data in a [[DataFrame]].
  + * A column that will be computed based on the data in a `DataFrame`.
  ```

- Fix throws annotations so that they are recognisable in javadoc

- Fix URL links to `<a href="http..."></a>`.

  ```diff
  - * [[http://en.wikipedia.org/wiki/Decision_tree_learning Decision tree]] model for regression.
  + * <a href="http://en.wikipedia.org/wiki/Decision_tree_learning">
  + * Decision tree (Wikipedia)</a> model for regression.
  ```

  ```diff
  -   * see http://en.wikipedia.org/wiki/Receiver_operating_characteristic
  +   * see <a href="http://en.wikipedia.org/wiki/Receiver_operating_characteristic">
  +   * Receiver operating characteristic (Wikipedia)</a>
  ```

- Fix < to > to

  - `greater than`/`greater than or equal to` or `less than`/`less than or equal to` where applicable.

  - Wrap it with `{{{...}}}` to print them in javadoc or use `{code ...}` or `{literal ..}`. Please refer https://github.com/apache/spark/pull/16013#discussion_r89665558

- Fix `</p>` complaint

## How was this patch tested?

Manually tested by `jekyll build` with Java 7 and 8

```
java version "1.7.0_80"
Java(TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)
```

```
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
```

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #16013 from HyukjinKwon/SPARK-3359-errors-more.

4 files changed, 27 insertions, 15 deletions

diff --git a/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaCluster.scala b/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaCluster.scala
index 35acb7b09f..e0e44d4440 100644
--- a/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaCluster.scala
+++ b/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaCluster.scala
@@ -231,7 +231,10 @@ class KafkaCluster(val kafkaParams: Map[String, String]) extends Serializable {
   // this 0 here indicates api version, in this case the original ZK backed api.
   private def defaultConsumerApiVersion: Short = 0
 
-  /** Requires Kafka >= 0.8.1.1.  Defaults to the original ZooKeeper backed api version. */
+  /**
+   * Requires Kafka 0.8.1.1 or later.
+   * Defaults to the original ZooKeeper backed API version.
+   */
   def getConsumerOffsets(
       groupId: String,
       topicAndPartitions: Set[TopicAndPartition]
@@ -250,7 +253,10 @@ class KafkaCluster(val kafkaParams: Map[String, String]) extends Serializable {
     }
   }
 
-  /** Requires Kafka >= 0.8.1.1.  Defaults to the original ZooKeeper backed api version. */
+  /**
+   * Requires Kafka 0.8.1.1 or later.
+   * Defaults to the original ZooKeeper backed API version.
+   */
   def getConsumerOffsetMetadata(
       groupId: String,
       topicAndPartitions: Set[TopicAndPartition]
@@ -287,7 +293,10 @@ class KafkaCluster(val kafkaParams: Map[String, String]) extends Serializable {
     Left(errs)
   }
 
-  /** Requires Kafka >= 0.8.1.1.  Defaults to the original ZooKeeper backed api version. */
+  /**
+   * Requires Kafka 0.8.1.1 or later.
+   * Defaults to the original ZooKeeper backed API version.
+   */
   def setConsumerOffsets(
       groupId: String,
       offsets: Map[TopicAndPartition, Long]
@@ -305,7 +314,10 @@ class KafkaCluster(val kafkaParams: Map[String, String]) extends Serializable {
     setConsumerOffsetMetadata(groupId, meta, consumerApiVersion)
   }
 
-  /** Requires Kafka >= 0.8.1.1.  Defaults to the original ZooKeeper backed api version. */
+  /**
+   * Requires Kafka 0.8.1.1 or later.
+   * Defaults to the original ZooKeeper backed API version.
+   */
   def setConsumerOffsetMetadata(
       groupId: String,
       metadata: Map[TopicAndPartition, OffsetAndMetadata]
diff --git a/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaInputDStream.scala b/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaInputDStream.scala
index 3713bda41b..7ff3a98ca5 100644
--- a/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaInputDStream.scala
+++ b/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaInputDStream.scala
@@ -38,7 +38,7 @@ import org.apache.spark.util.ThreadUtils
  *
  * @param kafkaParams Map of kafka configuration parameters.
  *                    See: http://kafka.apache.org/configuration.html
- * @param topics Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+ * @param topics Map of (topic_name to numPartitions) to consume. Each partition is consumed
  * in its own thread.
  * @param storageLevel RDD storage level.
  */
diff --git a/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaUtils.scala b/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaUtils.scala
index 56f0cb0b16..d5aef8184f 100644
--- a/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaUtils.scala
+++ b/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/KafkaUtils.scala
@@ -47,7 +47,7 @@ object KafkaUtils {
    * @param ssc       StreamingContext object
    * @param zkQuorum  Zookeeper quorum (hostname:port,hostname:port,..)
    * @param groupId   The group id for this consumer
-   * @param topics    Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   * @param topics    Map of (topic_name to numPartitions) to consume. Each partition is consumed
    *                  in its own thread
    * @param storageLevel  Storage level to use for storing the received objects
    *                      (default: StorageLevel.MEMORY_AND_DISK_SER_2)
@@ -72,7 +72,7 @@ object KafkaUtils {
    * @param ssc         StreamingContext object
    * @param kafkaParams Map of kafka configuration parameters,
    *                    see http://kafka.apache.org/08/configuration.html
-   * @param topics      Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   * @param topics      Map of (topic_name to numPartitions) to consume. Each partition is consumed
    *                    in its own thread.
    * @param storageLevel Storage level to use for storing the received objects
    * @tparam K type of Kafka message key
@@ -97,7 +97,7 @@ object KafkaUtils {
    * @param jssc      JavaStreamingContext object
    * @param zkQuorum  Zookeeper quorum (hostname:port,hostname:port,..)
    * @param groupId   The group id for this consumer
-   * @param topics    Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   * @param topics    Map of (topic_name to numPartitions) to consume. Each partition is consumed
    *                  in its own thread
    * @return DStream of (Kafka message key, Kafka message value)
    */
@@ -115,7 +115,7 @@ object KafkaUtils {
    * @param jssc      JavaStreamingContext object
    * @param zkQuorum  Zookeeper quorum (hostname:port,hostname:port,..).
    * @param groupId   The group id for this consumer.
-   * @param topics    Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   * @param topics    Map of (topic_name to numPartitions) to consume. Each partition is consumed
    *                  in its own thread.
    * @param storageLevel RDD storage level.
    * @return DStream of (Kafka message key, Kafka message value)
@@ -140,7 +140,7 @@ object KafkaUtils {
    * @param valueDecoderClass Type of kafka value decoder
    * @param kafkaParams Map of kafka configuration parameters,
    *                    see http://kafka.apache.org/08/configuration.html
-   * @param topics  Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   * @param topics  Map of (topic_name to numPartitions) to consume. Each partition is consumed
    *                in its own thread
    * @param storageLevel RDD storage level.
    * @tparam K type of Kafka message key
@@ -396,7 +396,7 @@ object KafkaUtils {
    *    You can access the offsets used in each batch from the generated RDDs (see
    *    [[org.apache.spark.streaming.kafka.HasOffsetRanges]]).
    *  - Failure Recovery: To recover from driver failures, you have to enable checkpointing
-   *    in the [[StreamingContext]]. The information on consumed offset can be
+   *    in the `StreamingContext`. The information on consumed offset can be
    *    recovered from the checkpoint. See the programming guide for details (constraints, etc.).
    *  - End-to-end semantics: This stream ensures that every records is effectively received and
    *    transformed exactly once, but gives no guarantees on whether the transformed data are
@@ -448,7 +448,7 @@ object KafkaUtils {
    *    You can access the offsets used in each batch from the generated RDDs (see
    *    [[org.apache.spark.streaming.kafka.HasOffsetRanges]]).
    *  - Failure Recovery: To recover from driver failures, you have to enable checkpointing
-   *    in the [[StreamingContext]]. The information on consumed offset can be
+   *    in the `StreamingContext`. The information on consumed offset can be
    *    recovered from the checkpoint. See the programming guide for details (constraints, etc.).
    *  - End-to-end semantics: This stream ensures that every records is effectively received and
    *    transformed exactly once, but gives no guarantees on whether the transformed data are
@@ -499,7 +499,7 @@ object KafkaUtils {
    *    You can access the offsets used in each batch from the generated RDDs (see
    *    [[org.apache.spark.streaming.kafka.HasOffsetRanges]]).
    *  - Failure Recovery: To recover from driver failures, you have to enable checkpointing
-   *    in the [[StreamingContext]]. The information on consumed offset can be
+   *    in the `StreamingContext`. The information on consumed offset can be
    *    recovered from the checkpoint. See the programming guide for details (constraints, etc.).
    *  - End-to-end semantics: This stream ensures that every records is effectively received and
    *    transformed exactly once, but gives no guarantees on whether the transformed data are
@@ -565,7 +565,7 @@ object KafkaUtils {
    *    You can access the offsets used in each batch from the generated RDDs (see
    *    [[org.apache.spark.streaming.kafka.HasOffsetRanges]]).
    *  - Failure Recovery: To recover from driver failures, you have to enable checkpointing
-   *    in the [[StreamingContext]]. The information on consumed offset can be
+   *    in the `StreamingContext`. The information on consumed offset can be
    *    recovered from the checkpoint. See the programming guide for details (constraints, etc.).
    *  - End-to-end semantics: This stream ensures that every records is effectively received and
    *    transformed exactly once, but gives no guarantees on whether the transformed data are
diff --git a/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/OffsetRange.scala b/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/OffsetRange.scala
index d9b856e469..10d364f987 100644
--- a/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/OffsetRange.scala
+++ b/external/kafka-0-8/src/main/scala/org/apache/spark/streaming/kafka/OffsetRange.scala
@@ -22,7 +22,7 @@ import kafka.common.TopicAndPartition
 /**
  * Represents any object that has a collection of [[OffsetRange]]s. This can be used to access the
  * offset ranges in RDDs generated by the direct Kafka DStream (see
- * [[KafkaUtils.createDirectStream()]]).
+ * `KafkaUtils.createDirectStream()`).
  * {{{
  *   KafkaUtils.createDirectStream(...).foreachRDD { rdd =>
  *      val offsetRanges = rdd.asInstanceOf[HasOffsetRanges].offsetRanges