[SPARK-3573][MLLIB] Make MLlib's Vector compatible with SQL's SchemaRDD

Register MLlib's Vector as a SQL user-defined type (UDT) in both Scala and Python. With this PR, we can easily map a RDD[LabeledPoint] to a SchemaRDD, and then select columns or save to a Parquet file. Examples in Scala/Python are attached. The Scala code was copied from jkbradley.

~~This PR contains the changes from #3068 . I will rebase after #3068 is merged.~~

marmbrus jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #3070 from mengxr/SPARK-3573 and squashes the following commits:

3a0b6e5 [Xiangrui Meng] organize imports
236f0a0 [Xiangrui Meng] register vector as UDT and provide dataset examples
[SPARK-4163][Core] Add a backward compatibility test for FetchFailed

/cc aarondav

Author: zsxwing <zsxwing@gmail.com>

Closes #3086 from zsxwing/SPARK-4163-back-comp and squashes the following commits:

21cb2a8 [zsxwing] Add a backward compatibility test for FetchFailed
[SPARK-4166][Core] Add a backward compatibility test for ExecutorLostFailure

Author: zsxwing <zsxwing@gmail.com>

Closes #3085 from zsxwing/SPARK-4166-back-comp and squashes the following commits:

89329f4 [zsxwing] Add a backward compatibility test for ExecutorLostFailure
[SPARK-3886] [PySpark] simplify serializer, use AutoBatchedSerializer by default.

This PR simplify serializer, always use batched serializer (AutoBatchedSerializer as default), even batch size is 1.

Author: Davies Liu <davies@databricks.com>

This patch had conflicts when merged, resolved by
Committer: Josh Rosen <joshrosen@databricks.com>

Closes #2920 from davies/fix_autobatch and squashes the following commits:

e544ef9 [Davies Liu] revert unrelated change
6880b14 [Davies Liu] Merge branch 'master' of github.com:apache/spark into fix_autobatch
1d557fc [Davies Liu] fix tests
8180907 [Davies Liu] Merge branch 'master' of github.com:apache/spark into fix_autobatch
76abdce [Davies Liu] clean up
53fa60b [Davies Liu] Merge branch 'master' of github.com:apache/spark into fix_autobatch
d7ac751 [Davies Liu] Merge branch 'master' of github.com:apache/spark into fix_autobatch
2cc2497 [Davies Liu] Merge branch 'master' of github.com:apache/spark into fix_autobatch
b4292ce [Davies Liu] fix bug in master
d79744c [Davies Liu] recover hive tests
be37ece [Davies Liu] refactor
eb3938d [Davies Liu] refactor serializer in scala
8d77ef2 [Davies Liu] simplify serializer, use AutoBatchedSerializer by default.