BytesReference should be a really simple interface, yet it has a gazillion
ways to achieve the same this. Methods like `#hasArray`, `#toBytesArray`, `#copyBytesArray`
`#toBytesRef` `#bytes` are all really duplicates. This change simplifies the interface
dramatically and makes implementations of it much simpler. All array access has been removed
and is streamlined through a single `#toBytesRef` method. Utility methods to materialize a
compact byte array has been added too for convenience.
5c8164a561