Need to mark codec-related definitions for export #2881
Description
The following definitions need to be exported in order to land w3c/webrtc-encoded-transform#186 with the right links:
- final steps to create an offer
- final steps to create an answer
- list of implemented receive codecs (which should also be marked as an RTCRtpReceiver property, to match the list of implemented send codecs anchor)
The WEBRTC-PC spec also refers to "list of codecs which the user agent is currently prepared to receive" and "list of codecs which the user agent is currently capable of sending"; these terms are not tagged or defined further. We might want to add definitions for these.