Summary:
As a first step of supporting user-defined timestamps with ingestion, the
patch adds timestamp support to `SstFileWriter`; namely, it adds new
versions of the `Put` and `Delete` APIs that take timestamps. (`Merge`
and `DeleteRange` are currently not supported with user-defined timestamps
in general but once those features are implemented, we can handle them
in `SstFileWriter` in a similar fashion.) The new APIs validate the size of
the timestamp provided by the client. Similarly, calls to the pre-existing
timestamp-less APIs are now disallowed when user-defined timestamps are
in use according to the comparator.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8899

Test Plan: `make check`

Reviewed By: riversand963

Differential Revision: D30850699

Pulled By: ltamasi

fbshipit-source-id: 779154373618f19b8f0797976bb7286783c57b67