[SPARK-19402][DOCS] Support LaTex inline formula correctly and fix warnings in Scala/Java APIs generation

## What changes were proposed in this pull request?

This PR proposes three things as below:

- Support LaTex inline-formula, `\( ... \)` in Scala API documentation
  It seems currently,

  ```
  \( ... \)
  ```

  are rendered as they are, for example,

  <img width="345" alt="2017-01-30 10 01 13" src="https://cloud.githubusercontent.com/assets/6477701/22423960/ab37d54a-e737-11e6-9196-4f6229c0189c.png">

  It seems mistakenly more backslashes were added.

- Fix warnings Scaladoc/Javadoc generation
  This PR fixes t two types of warnings as below:

  ```
  [warn] .../spark/sql/catalyst/src/main/scala/org/apache/spark/sql/Row.scala:335: Could not find any member to link for "UnsupportedOperationException".
  [warn]   /**
  [warn]   ^
  ```

  ```
  [warn] .../spark/sql/core/src/main/scala/org/apache/spark/sql/internal/VariableSubstitution.scala:24: Variable var undefined in comment for class VariableSubstitution in class VariableSubstitution
  [warn]  * `${var}`, `${system:var}` and `${env:var}`.
  [warn]      ^
  ```

- Fix Javadoc8 break
  ```
  [error] .../spark/mllib/target/java/org/apache/spark/ml/PredictionModel.java:7: error: reference not found
  [error]  *                       E.g., {link VectorUDT} for vector features.
  [error]                                       ^
  [error] .../spark/mllib/target/java/org/apache/spark/ml/PredictorParams.java:12: error: reference not found
  [error]    *                          E.g., {link VectorUDT} for vector features.
  [error]                                            ^
  [error] .../spark/mllib/target/java/org/apache/spark/ml/Predictor.java:10: error: reference not found
  [error]  *                       E.g., {link VectorUDT} for vector features.
  [error]                                       ^
  [error] .../spark/sql/hive/target/java/org/apache/spark/sql/hive/HiveAnalysis.java:5: error: reference not found
  [error]  * Note that, this rule must be run after {link PreprocessTableInsertion}.
  [error]                                                  ^
  ```

## How was this patch tested?

Manually via `sbt unidoc` and `jeykil build`.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #16741 from HyukjinKwon/warn-and-break.

3 files changed, 4 insertions, 4 deletions

diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveInspectors.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveInspectors.scala
index 52aa1088ac..21b729bf29 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveInspectors.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveInspectors.scala
@@ -772,7 +772,7 @@ private[hive] trait HiveInspectors {
 
   /**
    * Map the catalyst expression to ObjectInspector, however,
-   * if the expression is [[Literal]] or foldable, a constant writable object inspector returns;
+   * if the expression is `Literal` or foldable, a constant writable object inspector returns;
    * Otherwise, we always get the object inspector according to its data type(in catalyst)
    * @param expr Catalyst expression to be mapped
    * @return Hive java objectinspector (recursively).
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala
index badccae168..39be41770d 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala
@@ -80,7 +80,7 @@ class DetermineHiveSerde(conf: SQLConf) extends Rule[LogicalPlan] {
 /**
  * Replaces generic operations with specific variants that are designed to work with Hive.
  *
- * Note that, this rule must be run after [[PreprocessTableInsertion]].
+ * Note that, this rule must be run after `PreprocessTableInsertion`.
  */
 class HiveAnalysis(session: SparkSession) extends Rule[LogicalPlan] {
   override def apply(plan: LogicalPlan): LogicalPlan = plan resolveOperators {
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/execution/InsertIntoHiveTable.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/execution/InsertIntoHiveTable.scala
index ce418ae135..3e654d8eeb 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/execution/InsertIntoHiveTable.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/execution/InsertIntoHiveTable.scala
@@ -50,10 +50,10 @@ import org.apache.spark.SparkException
  * blame Reynold for this! He was just moving code around!
  *
  * In the future we should converge the write path for Hive with the normal data source write path,
- * as defined in [[org.apache.spark.sql.execution.datasources.FileFormatWriter]].
+ * as defined in `org.apache.spark.sql.execution.datasources.FileFormatWriter`.
  *
  * @param table the logical plan representing the table. In the future this should be a
- *              [[org.apache.spark.sql.catalyst.catalog.CatalogTable]] once we converge Hive tables
+ *              `org.apache.spark.sql.catalyst.catalog.CatalogTable` once we converge Hive tables
  *              and data source tables.
  * @param partition a map from the partition key to the partition value (optional). If the partition
  *                  value is optional, dynamic partition insert will be performed.