Summary:
This PR adds support to programmatically iterate a raw table file with an iterator returned by `SstFileReader::NewTableIterator`. For third party tools to use to observe SST files created by RocksDB.
The original feature request was from this merge request: https://github.com/facebook/rocksdb/pull/12370
Since keys returned by raw table iterators are internal keys, this PR also adds a struct `ParsedEntryInfo` and util method `ParseEntry` to support user to parse internal key. `GetInternalKeyForSeek`, and `GetInternalKeyForSeekForPrev` to support users to create internal keys for seek operations with this raw table iterator.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12385
Test Plan: Added unit tests
Reviewed By: cbi42
Differential Revision: D55662855
Pulled By: jowlyzhang
fbshipit-source-id: 0716a173ee95924fbd4e1f9b6cccf06525c40049
Yu Zhang