Comparator: Add func: IsBytewiseComparator & IsReverseBytewiseComparator

[rockeet]

This was a PR to upstream facebook/rocksdb#10645

Copied from facebook/rocksdb#10645

Virtual function call to comparator is very frequent thus is a hot spot
In most use cases, the default BytewiseComparator or ReverseBytewiseComparator is used
This PR provide the basic support for our later PRs for FindFileInRange and MergingIterator:

devirtualize such virtual functions calls for BytewiseComparator or ReverseBytewiseComparator
Add prefix cache to omit most memcmp and indirect memory access to key
Performance of FindFileInRange was improved 20x+, MergingIterator was improved 3x+.

see PR: facebook/rocksdb#10646 FindFileInRange devirtualization and prefix cache

PR MergingIterator depends on PR facebook/rocksdb#9035 thus we would create it later.

Relevant commits

331715c leipeng 2022-09-19 19:26:36 +0800 Add Comparator::opt_cmp_type()
9327631 leipeng 2022-07-21 15:06:55 +0800 Merge branch 'sideplugin-7.04.0-415200d7' into sideplugin-7.06.0-a0c63083
27a169f leipeng 2022-06-20 21:40:41 +0800 IsBytewiseComparator: optimize add cmp type to Comparator
f033dac leipeng 2022-06-16 22:56:59 +0800 Add IsReverseBytewiseComparator()
5c62088 leipeng 2022-06-09 18:37:24 +0800 Merge branch 'sideplugin-7.01.0-a5e51305' into sideplugin-7.03.0-f85b31a2
b65e06f leipeng 2022-03-30 11:21:17 +0800 Merge branch 'sideplugin-6.28.0-677d2b4a' into sideplugin-7.01.0-a5e51305
de07870 leipeng 2021-12-31 14:35:01 +0800 Merge branch 'sideplugin-6.26.0-28bab0ef' into sideplugin-6.28.0-677d2b4a
8287e70 leipeng 2021-12-11 12:53:05 +0800 Move IsBytewiseComparator ... from topling-rocks to toplingdb repo