ARROW-12138: [Go][IPC] Update flatbuffers definitions

[zeroshade]

Updating the generated flatbuffer code so that newer features like compression in IPC can get implemented. Doing the updating of the flatbuffer generated code first as a separate change.

@sbinet @emkornfield

[zeroshade]

All that was done for this change was to run go run ./gen-flatbuffers.go followed by updating the couple of files in the ipc module which had to switch direct references to byte or int16 to the exported types from the flatbuffers files. So the only files in this change that contain anything that wasn't generated by flatc are ipc/file_writer.go, ipc/message.go and ipc/metadata.go. Everything else just contains the generated flatbuffer code.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-12138

[zeroshade]

@sbinet @emkornfield @wesm once this is merged, i have a PR ready for adding compression handling to the go IPC implementation, I'm just waiting for this to get merged before filing it for ease of review