Transcoder: Allow setting operating rate and priority on both encoder and decoder

Plumb through operating rate and priority to both codecs when
configuring the video track transcoder.

Fixes: 169719271
Test: Unit test, manually verifying the settings and benchmarking.
Change-Id: I229eaaf0ae0d5002e2eec52eb83a6bb92694b1d2
5 files changed