[SPARK-3935][Core] log the number of records that has been written

There is a unused variable(count) in saveAsHadoopDataset in PairRDDFunctions.scala. The initial idea of this variable seems to count the number of records, so I am adding a log statement to log the number of records that has been written to the writer.

Author: likun <jacky.likun@huawei.com>
Author: jackylk <jacky.likun@huawei.com>

Closes #2791 from jackylk/SPARK-3935 and squashes the following commits:

a874047 [jackylk] removing the unused variable in PairRddFunctions.scala
3bf43c7 [likun] log the number of records has been written
[SPARK-3979] [yarn] Use fs's default replication.

This avoids issues when HDFS is configured in a way that would not
allow the hardcoded default replication of "3".

Note: getDefaultReplication(Path) was added in 0.23.3, and the oldest
one available on Maven Central is 0.23.7, so I chose to not add code
to access that method via reflection.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #2831 from vanzin/SPARK-3979 and squashes the following commits:

b0e3a97 [Marcelo Vanzin] [SPARK-3979] [yarn] Use fs's default replication.
[SPARK-3855][SQL] Preserve the result attribute of python UDFs though transformations

In the current implementation it was possible for the reference to change after analysis.

Author: Michael Armbrust <michael@databricks.com>

Closes #2717 from marmbrus/pythonUdfResults and squashes the following commits:

da14879 [Michael Armbrust] Fix test
6343bcb [Michael Armbrust] add test
9533286 [Michael Armbrust] Correctly preserve the result attribute of python UDFs though transformations
[SPARK-3985] [Examples] fix file path using os.path.join

Author: Daoyuan Wang <daoyuan.wang@intel.com>

Closes #2834 from adrian-wang/sqlpypath and squashes the following commits:

da7aa95 [Daoyuan Wang] fix file path using path.join
[SPARK-3934] [SPARK-3918] [mllib]  Bug fixes for RandomForest, DecisionTree

SPARK-3934: When run with a mix of unordered categorical and continuous features, on multiclass classification, RandomForest fails. The bug is in the sanity checks in getFeatureOffset and getLeftRightFeatureOffsets, which use the wrong indices for checking whether features are unordered.
Fix: Remove the sanity checks since they are not really needed, and since they would require DTStatsAggregator to keep track of an extra set of indices (for the feature subset).

Added test to RandomForestSuite which failed with old version but now works.

SPARK-3918: Added baggedInput.unpersist at end of training.

Also:
* I removed DTStatsAggregator.isUnordered since it is no longer used.
* DecisionTreeMetadata: Added logWarning when maxBins is automatically reduced.
* Updated DecisionTreeRunner to explicitly fix the test data to have the same number of features as the training data.  This is a temporary fix which should eventually be replaced by pre-indexing both datasets.
* RandomForestModel: Updated toString to print total number of nodes in forest.
* Changed Predict class to be public DeveloperApi.  This was necessary to allow users to create their own trees by hand (for testing).

CC: mengxr  manishamde chouqin codedeft  Just notifying you of these small bug fixes.

Author: Joseph K. Bradley <joseph.kurata.bradley@gmail.com>

Closes #2785 from jkbradley/dtrunner-update and squashes the following commits:

9132321 [Joseph K. Bradley] merged with master, fixed imports
9dbd000 [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
e116473 [Joseph K. Bradley] Changed Predict class to be public DeveloperApi.
f502e65 [Joseph K. Bradley] bug fix for SPARK-3934
7f3d60f [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
ba567ab [Joseph K. Bradley] Changed DTRunner to load test data using same number of features as in training data.
4e88c1f [Joseph K. Bradley] changed RF toString to print total number of nodes