Redefine SendCodecs and ReceiveCodecs

[alvestrand]

to contain all supported codecs, revealing only those that are "enabled" at any given time.

Fixes: #2925

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[alvestrand]

Not sure "editorial" is correct here. It does document the existing browser behavior that implemented but not announced codecs are revealed when they are specifically asked for. But it unblocks the check.

[alvestrand]

WG discussion on Feb 20, 2024: Looks like an improvement.

[dontcallmedom-bot]

This issue had an associated resolution in WebRTC February 2024 meeting – 20 February 2024 (Modify the codec description model to ease describing changes #2925 #2935):

RESOLUTION: Bring #2935 for merging to editors meeting

[alvestrand]

From @jan-ivar : link definition of "enabled" to a dfn so that what it is is defined in one place.

[alvestrand]

Hoisting the @dontcallmedom flag. Can't figure out how to run respec locally to get the error message that listAmendments is complaining about.

[dontcallmedom]

FYI: what was missing was the step of 1 of the amendment markup process - adding the id of the changed section to base-rec.html.

[alvestrand]

Thank you @dontcallmedom ! (and for reminding me of the documentation link!!)

[dontcallmedom]

are there tests associated with this pull request? I would document them in #2910 (and if not, we should track the need to create them)