Add support for hijacking exception type
Add support for hijacking exception type

Summary:
When a Stream instance is completed with an error, this error will be sent from a server to a client via onError method.
This error will be encoded on the server and decoded on the client.

This new function, errorMap, will perform this encoding and decoding steps.

Reviewed By: yfeldblum

Differential Revision: D8462386

fbshipit-source-id: d2a501da326f92ce60fa755574c4e39496a0f576

rsocket/rsocket-cpp,rsocket/rsocket-cpp,phoad/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,phoad/rsocket-cpp,phoad/rsocket-cpp,phoad/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,phoad/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,rsocket/rsocket-cpp,rsocket/rsocket-cpp