DRILL-7439: Batch count fixes for six additional operators
Enables vector checks, and fixes batch count and vector issues for:
* StreamingAggBatch
* RuntimeFilterRecordBatch
* FlattenRecordBatch
* MergeJoinBatch
* NestedLoopJoinBatch
* LimitRecordBatch
Also fixes a zero-size batch validity issue for the CSV reader when
all files contain no data.
Includes code cleanup for files touched in this PR.
closes #1893
