Summary:
The patch cleans up and refactors `CompressBlock` and `CompressBlockInternal` a bit.
In particular, it does the following:
* It renames `CompressBlockInternal` to `CompressData` and moves it to `util/compression.h`,
where other general compression-related utilities are located. This will facilitate reuse in the
BlobDB write path.
* The signature of the method is changed so it now takes `compression_format_version`
(similarly to the compression library specific methods) instead of `format_version` (which is
specific to the block based table).
* `GetCompressionFormatForVersion` no longer takes `compression_type` as a parameter.
This parameter was only used in a (not entirely up-to-date) assertion; also, removing it
eliminates the need to ensure this precondition holds at all call sites.
* Does some minor cleanup in `CompressBlock`, for instance, it is now possible to pass
only one of `sampled_output_fast` and `sampled_output_slow`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7249
Test Plan: `make check`
Reviewed By: riversand963
Differential Revision: D23087278
Pulled By: ltamasi
fbshipit-source-id: e6316e45baed8b4e7de7c1780c90501c2a3439b3
9d6f48ec1d