Replace UsedPayloadTypes with PayloadTypeSuggester in CodecVendor.

This CL removes the legacy UsedPayloadTypes and UsedIds classes, as
their functionality is now fully covered by PayloadTypeSuggester.

Key changes:
- pc/codec_vendor.cc now uses the provided PayloadTypeSuggester to avoid
  payload type collisions when building offers.
- PayloadTypeSuggester and PayloadTypePicker now support
  'pick_from_top_of_range' to maintain the existing behavior of
  allocating colliding PTs from the top of the dynamic range.
- SdpPayloadTypeSuggester and FakePayloadTypeSuggester now record
  suggested mappings immediately to prevent collisions within the same
  negotiation.
- Updated compatibility checks to use MatchesWithReferenceAttributes
  to correctly handle RTX codecs.
- Cleaned up related BUILD.gn targets, documentation, and comments.

Bug: webrtc:360058654
Change-Id: Ia36d6b342c2442ccfd8548a2731388646495c3c8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/471800
Auto-Submit: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47692}