### What changes were proposed in this pull request?
This is followup from https://github.com/apache/spark/pull/29342, where to do two things:
* Per https://github.com/apache/spark/pull/29342#discussion_r470153323, change from java `HashSet` to spark in-house `OpenHashSet` to track matched rows for non-unique join keys. I checked `OpenHashSet` implementation which is built from a key index (`OpenHashSet._bitset` as `BitSet`) and key array (`OpenHashSet._data` as `Array`). Java `HashSet` is built from `HashMap`, which stores value in `Node` linked list and by theory should have taken more memory than `OpenHashSet`. Reran the same benchmark query used in https://github.com/apache/spark/pull/29342, and verified the query has similar performance here between `HashSet` and `OpenHashSet`.
* Track metrics of the extra data structure `BitSet`/`OpenHashSet` for full outer SHJ. This depends on above thing, because there seems no easy way to get java `HashSet` memory size.
### Why are the changes needed?
To better surface the memory usage for full outer SHJ more accurately.
This can help users/developers to debug/improve full outer SHJ.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Added unite test in `SQLMetricsSuite.scala` .
Closes#29566 from c21/add-metrics.
Authored-by: Cheng Su <chengsu@fb.com>
Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>
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