[SPARK-3519] add distinct(n) to PySpark

Added missing rdd.distinct(numPartitions) and associated tests

Author: Matthew Farrellee <matt@redhat.com>

Closes #2383 from mattf/SPARK-3519 and squashes the following commits:

30b837a [Matthew Farrellee] Combine test cases to save on JVM startups
6bc4a2c [Matthew Farrellee] [SPARK-3519] add distinct(n) to SchemaRDD in PySpark
7a17f2b [Matthew Farrellee] [SPARK-3519] add distinct(n) to PySpark
[SPARK-3308][SQL] Ability to read JSON Arrays as tables

This PR aims to support reading top level JSON arrays and take every element in such an array as a row (an empty array will not generate a row).

JIRA: https://issues.apache.org/jira/browse/SPARK-3308

Author: Yin Huai <huai@cse.ohio-state.edu>

Closes #2400 from yhuai/SPARK-3308 and squashes the following commits:

990077a [Yin Huai] Handle top level JSON arrays.