Summary:
Similar to point tombstones, we can drop a range tombstone during compaction when we know its range does not exist in any higher level. This PR adds this optimization. Some existing test in db_range_del_test is fixed to work under this optimization.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11459

Test Plan:
* Add unit test `DBRangeDelTest, NonBottommostCompactionDropRangetombstone`.
* Ran crash test that issues range deletion for a few hours: `python3 tools/db_crashtest.py blackbox --simple --write_buffer_size=1048576 --delrangepercent=10 --writepercent=31 --readpercent=40`

Reviewed By: ajkr

Differential Revision: D46007904

Pulled By: cbi42

fbshipit-source-id: 3f37205b6778b7d55ed106369ca41b0632a6d0fd