[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, 7 insertions, 7 deletions

diff --git a/streaming/src/main/scala/org/apache/spark/streaming/StateSpec.scala b/streaming/src/main/scala/org/apache/spark/streaming/StateSpec.scala
index 7c1ea2f89d..c3b28bd516 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/StateSpec.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/StateSpec.scala
@@ -30,7 +30,7 @@ import org.apache.spark.util.ClosureCleaner
  * `mapWithState` operation of a
  * [[org.apache.spark.streaming.dstream.PairDStreamFunctions pair DStream]] (Scala) or a
  * [[org.apache.spark.streaming.api.java.JavaPairDStream JavaPairDStream]] (Java).
- * Use [[org.apache.spark.streaming.StateSpec.function() StateSpec.function]] factory methods
+ * Use `org.apache.spark.streaming.StateSpec.function()` factory methods
  * to create instances of this class.
  *
  * Example in Scala:
@@ -100,7 +100,7 @@ sealed abstract class StateSpec[KeyType, ValueType, StateType, MappedType] exten
 
 /**
  * :: Experimental ::
- * Builder object for creating instances of [[org.apache.spark.streaming.StateSpec StateSpec]]
+ * Builder object for creating instances of `org.apache.spark.streaming.StateSpec`
  * that is used for specifying the parameters of the DStream transformation `mapWithState`
  * that is used for specifying the parameters of the DStream transformation
  * `mapWithState` operation of a
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaPairDStream.scala b/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaPairDStream.scala
index aa4003c62e..2ec907c8cf 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaPairDStream.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaPairDStream.scala
@@ -434,8 +434,8 @@ class JavaPairDStream[K, V](val dstream: DStream[(K, V)])(
    * Return a [[JavaMapWithStateDStream]] by applying a function to every key-value element of
    * `this` stream, while maintaining some state data for each unique key. The mapping function
    * and other specification (e.g. partitioners, timeouts, initial state data, etc.) of this
-   * transformation can be specified using [[StateSpec]] class. The state data is accessible in
-   * as a parameter of type [[State]] in the mapping function.
+   * transformation can be specified using `StateSpec` class. The state data is accessible in
+   * as a parameter of type `State` in the mapping function.
    *
    * Example of using `mapWithState`:
    * {{{
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaStreamingContext.scala b/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaStreamingContext.scala
index b43b9405de..982e72cffb 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaStreamingContext.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaStreamingContext.scala
@@ -44,7 +44,7 @@ import org.apache.spark.streaming.scheduler.StreamingListener
  * A Java-friendly version of [[org.apache.spark.streaming.StreamingContext]] which is the main
  * entry point for Spark Streaming functionality. It provides methods to create
  * [[org.apache.spark.streaming.api.java.JavaDStream]] and
- * [[org.apache.spark.streaming.api.java.JavaPairDStream.]] from input sources. The internal
+ * [[org.apache.spark.streaming.api.java.JavaPairDStream]] from input sources. The internal
  * org.apache.spark.api.java.JavaSparkContext (see core Spark documentation) can be accessed
  * using `context.sparkContext`. After creating and transforming DStreams, the streaming
  * computation can be started and stopped using `context.start()` and `context.stop()`,
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/dstream/PairDStreamFunctions.scala b/streaming/src/main/scala/org/apache/spark/streaming/dstream/PairDStreamFunctions.scala
index ac739411fd..f38c1e7996 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/dstream/PairDStreamFunctions.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/dstream/PairDStreamFunctions.scala
@@ -356,8 +356,8 @@ class PairDStreamFunctions[K, V](self: DStream[(K, V)])
    * Return a [[MapWithStateDStream]] by applying a function to every key-value element of
    * `this` stream, while maintaining some state data for each unique key. The mapping function
    * and other specification (e.g. partitioners, timeouts, initial state data, etc.) of this
-   * transformation can be specified using [[StateSpec]] class. The state data is accessible in
-   * as a parameter of type [[State]] in the mapping function.
+   * transformation can be specified using `StateSpec` class. The state data is accessible in
+   * as a parameter of type `State` in the mapping function.
    *
    * Example of using `mapWithState`:
    * {{{