message: VCMEncodedFrame: add basic support for AV1.
  This change adds basic support for setting codecType kVideoCodecAV1 in
  VCMEncodedFrames.
  Cr-Commit-Position: refs/heads/master@{#33594}
diff: @@ -136,6 +136,10 @@ void VCMEncodedFrame::CopyCodecSpecific(const RTPVideoHeader* header) {
  _codecSpecificInfo.codecType = kVideoCodecH264;
  break;
  }
  + case kVideoCodecAV1: {
  + _codecSpecificInfo.codecType = kVideoCodecAV1;
  + break;
  + }
  default: {
  _codecSpecificInfo.codecType = kVideoCodecGeneric;
  break;
  