This CL removes the coupling of the VideoToolbox h264 implementation
to the generic h264 code. The files have been moved into sdb/obj/Framework
and all dependency on them has been removed from the rest of WebRTC.
We now add it as an external encoder via a factory supplied to the
CreatePeerConnectionFactory call. This also brings the iOS implementation
closer to what we do on Android for MediaCodec.
BUG=webrtc:6619
Review-Url: https://codereview.webrtc.org/2463313002
Cr-Commit-Position: refs/heads/master@{#14953}
6a5047dad3