Make LibWebRTCCodecs::Encoder::codecType libwebrtc agnostic
<rdar://problem/100403063>
Pull request: https://github.com/WebKit/WebKit/pull/4702
Committed 254913@main (34544074434b): <https://commits.webkit.org/254913@main> Reviewed commits have been landed. Closing PR #4702 and removing active labels.