also refactor the code to have FillSendCodecStats/FillReceiveCodecStats methods for similarity with the video engine code. BUG=webrtc:14808 Change-Id: Ib0687f36a4b4a71c849e0b4918e50592d7772ff8 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/290891 Reviewed-by: Jakob Ivarsson <jakobi@webrtc.org> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org> Commit-Queue: Philipp Hancke <phancke@microsoft.com> Cr-Commit-Position: refs/heads/main@{#39172}