[SPARK-18775][SQL] Limit the max number of records written per file

## What changes were proposed in this pull request?
Currently, Spark writes a single file out per task, sometimes leading to very large files. It would be great to have an option to limit the max number of records written per file in a task, to avoid humongous files.

This patch introduces a new write config option `maxRecordsPerFile` (default to a session-wide setting `spark.sql.files.maxRecordsPerFile`) that limits the max number of records written to a single file. A non-positive value indicates there is no limit (same behavior as not having this flag).

## How was this patch tested?
Added test cases in PartitionedWriteSuite for both dynamic partition insert and non-dynamic partition insert.

Author: Reynold Xin <rxin@databricks.com>

Closes #16204 from rxin/SPARK-18775.