as required by https://aomediacodec.github.io/av1-rtp-spec/#72-sdp-parameters Also unify usage of profile fmtp parameter. Most notably this causes SDP answers to include the default values. These default values correspond to libaom's default values for AV1E_SET_TARGET_SEQ_LEVEL_IDX, AV1E_SET_TIER_MASK as used in https://source.chromium.org/chromium/chromium/src/+/main:third_party/libaom/source/libaom/aom/aomcx.h and g_profile in aom_codec_enc_cfg https://source.chromium.org/chromium/chromium/src/+/main:third_party/libaom/source/libaom/aom/aom_encoder.h;l=415;drc=b58207f5aecc39db7d3da766e7d171e5d2c3598e Note: AV1 is inconsistently cased in variable/struct/method/class names. The canonical casing should probably be "Av1" since it is an acronym standing for "AOMedia Video 1". BUG=webrtc:15703 Change-Id: I11864b7666fea906cd1a0759c7ad45997beab90e Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/331360 Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Commit-Queue: Philipp Hancke <phancke@microsoft.com> Cr-Commit-Position: refs/heads/main@{#41654}