[SPARK-15543][SQL] Rename DefaultSources to make them more self-describing

## What changes were proposed in this pull request?
This patch renames various DefaultSources to make their names more self-describing. The choice of "DefaultSource" was from the days when we did not have a good way to specify short names.

They are now named:
- LibSVMFileFormat
- CSVFileFormat
- JdbcRelationProvider
- JsonFileFormat
- ParquetFileFormat
- TextFileFormat

Backward compatibility is maintained through aliasing.

## How was this patch tested?
Updated relevant test cases too.

Author: Reynold Xin <rxin@databricks.com>

Closes #13311 from rxin/SPARK-15543.

1 files changed, 6 insertions, 2 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/source/libsvm/LibSVMRelation.scala b/mllib/src/main/scala/org/apache/spark/ml/source/libsvm/LibSVMRelation.scala
index 5ba768d551..64ebf0c982 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/source/libsvm/LibSVMRelation.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/source/libsvm/LibSVMRelation.scala
@@ -90,7 +90,7 @@ private[libsvm] class LibSVMOutputWriter(
  *     .load("data/mllib/sample_libsvm_data.txt")
  *
  *   // Java
- *   DataFrame df = spark.read().format("libsvm")
+ *   Dataset<Row> df = spark.read().format("libsvm")
  *     .option("numFeatures, "780")
  *     .load("data/mllib/sample_libsvm_data.txt");
  * }}}
@@ -105,9 +105,13 @@ private[libsvm] class LibSVMOutputWriter(
  *  - "vectorType": feature vector type, "sparse" (default) or "dense".
  *
  *  @see [[https://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/ LIBSVM datasets]]
+ *
+ * Note that this class is public for documentation purpose. Please don't use this class directly.
+ * Rather, use the data source API as illustrated above.
  */
+// If this is moved or renamed, please update DataSource's backwardCompatibilityMap.
 @Since("1.6.0")
-class DefaultSource extends FileFormat with DataSourceRegister {
+class LibSVMFileFormat extends FileFormat with DataSourceRegister {
 
   @Since("1.6.0")
   override def shortName(): String = "libsvm"