Summary:
Extend Java RocksDB iterators to support indirect byte buffers, to add to the existing support for direct byte buffers.
Code to distinguish direct/indirect buffers is switched in Java, and a 2nd separate JNI call implemented to support indirect
buffers. Indirect support passes contained buffers using byte[]

There are some Java subclasses of iterator (WBWIIterator, SstFileReaderIterator) which also now have parallel JNI support functions implemented, along with direct/indirect switches in Java methods.

Closes https://github.com/facebook/rocksdb/issues/6282

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9222

Reviewed By: ajkr

Differential Revision: D35115283

Pulled By: jay-zhuang

fbshipit-source-id: f8d5d20b975aef700560fbcc99f707bb028dc42e