[Flight] C++ and Java implementations are incompatible

A C++ client cannot request streams from a Java service, nor can it decode the schema from GetFlightInfo.

Schema: in Java, GetFlightInfo encodes the schema directly via flatbuffers. C++ expects it to be encoded as an IPC message. This isn't a problem in Java as a method exists to decode such schemas, but in C++ the API for reading such a schema isn't really exposed. I'm willing to submit a patch for this, but it's not clear to me which scheme is preferred.

Streams: in Java, DoGet starts with an ArrowMessage containing a schema. C++ does not expect this and segfaults when it tries to decode the message as a record batch. Based on the presentations I've seen, I think C++ is in the wrong here; I have a patch to fix this that I could clean up and submit.