[PT Redesign] Implement late payload type allocation for video.

This CL implements the late payload type allocation strategy for video
codecs, matching the existing implementation for audio.

Key changes:
- Introduced CodecConfiguration and ResiliencyInfo to track codec
  metadata without pre-assigned payload types.
- Implemented MergeCodecsFromConfigurations in CodecVendor to expand
  media codecs into their resiliency counterparts (RTX, RED, FEC) and
  link them only after primary PTs are suggested.
- Extracted MergeCodecsByDirection to unify direction-based merging
  logic across offer and answer paths.
- Relaxed RTX matching in CodecComparators to support negotiation before
  PTs are fully linked.
- Updated all call sites in pc/ to handle refactored CodecVendor
  accessors.
- Added integration tests in
  pc/codec_vendor_redesign_unittest.cc.

This work allows payload types to be assigned permanently during
SetLocalDescription/SetRemoteDescription, improving stability across
renegotiations.

Bug: webrtc:360058654
Change-Id: Ifae3f3daca1b18a3ada2131a57046ce4ff3dcd36
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/472060
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47709}