Support tiering when file endpoints overlap (#10961)

Support tiering when file endpoints overlap (#10961)

Summary:
Enabled output to penultimate level when file endpoints overlap. This is probably only possible when range tombstones span files. Otherwise the overlapping files would all be included in the penultimate level inputs thanks to our atomic compaction unit logic.

Also, corrected `penultimate_output_range_type_`, which is a minor fix as it appears only used for logging.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10961

Test Plan: updated unit test

Reviewed By: cbi42

Differential Revision: D41370615

Pulled By: ajkr

fbshipit-source-id: 7e75ec369a3b41b8382b336446c81825a4c4f572