## What changes were proposed in this pull request?
This pr is to fix an issue occurred when resharding Kinesis streams; the resharding makes the KCL throw an exception because Spark does not checkpoint `SHARD_END` when finishing reading closed shards in `KinesisRecordProcessor#shutdown`. This bug finally leads to stopping subscribing new split (or merged) shards.

## How was this patch tested?
Added a test in `KinesisStreamSuite` to check if it works well when splitting/merging shards.

Author: Takeshi YAMAMURO <linguin.m.s@gmail.com>

Closes #16213 from maropu/SPARK-18020.