[WebCodecs] Implement pixel buffer conversion for video frames produced by libwebrtc VPX decoders
<rdar://problem/101534191>
Pull request: https://github.com/WebKit/WebKit/pull/5747
Committed 255958@main (21c5196e6d48): <https://commits.webkit.org/255958@main> Reviewed commits have been landed. Closing PR #5747 and removing active labels.