Summary:
1. I added PingCap's more up-to-date Rust Binding of RocksDB
2. I also added ObjectiveRocks which is a very nice binding for _both_ Swift and Objective-C
Closes https://github.com/facebook/rocksdb/pull/4065

Differential Revision: D8670340

Pulled By: siying

fbshipit-source-id: 3db28bf3a464c3e050df52cc92b19248b7f43944