Align spec /w codec direction decision

[henbos]

How to deal with codecs and directionality was discussed at TPAC 2024:

• Minutes
• Slides
• Recording

There was a strong preference for Proposal A, i.e. to "keep it simple": sendonly transceivers can do all send codecs, recvonly transcievers can do all receive codecs, and sendrecv transceivers can only do codecs and profiles that you can BOTH send AND receive with. So if you want to do fancy unidirectional codecs or profiles you use multiple m= sections.

Let this issue track making sure the spec aligns with Proposal A and allow us to merge other codec related issues as fixed by this issue