Summary:
* Address feedback from https://github.com/facebook/rocksdb/issues/14040
* Add additional test for MultiScan
* Fix a bug when del range and data are in same file for multi-scan
* Rewrite the cases need to be handled in SeekMultiScan
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14055
Test Plan: Unit test
Reviewed By: cbi42, anand1976
Differential Revision: D84851788
Pulled By: xingbowang
fbshipit-source-id: 0f69632733afb99685f6341badbf239681010c38