Implement WebCodecsVideoDecoder with GPUProcess backend
<rdar://problem/100760198>
Pull request: https://github.com/WebKit/WebKit/pull/4985
Committed 255215@main (fa141c1bec03): <https://commits.webkit.org/255215@main> Reviewed commits have been landed. Closing PR #4985 and removing active labels.
Broke a number of layout tests: https://results.webkit.org/?suite=layout-tests&suite=layout-tests&suite=layout-tests&suite=layout-tests&test=imported%2Fw3c%2Fweb-platform-tests%2Fwebcodecs%2Freconfiguring-encoder.https.any.worker.html%3Fh264_annexb&test=imported%2Fw3c%2Fweb-platform-tests%2Fwebcodecs%2Freconfiguring-encoder.https.any.html%3Fh264_annexb&test=imported%2Fw3c%2Fweb-platform-tests%2Fwebcodecs%2FvideoDecoder-codec-specific.https.any.html%3Fh264_annexb&test=imported%2Fw3c%2Fweb-platform-tests%2Fwebcodecs%2FvideoDecoder-codec-specific.https.any.worker.html%3Fh264_annexb imported/w3c/web-platform-tests/webcodecs/videoDecoder-codec-specific.https.any.html?h264_annexb imported/w3c/web-platform-tests/webcodecs/videoDecoder-codec-specific.https.any.html?h264_annexb imported/w3c/web-platform-tests/webcodecs/reconfiguring-encoder.https.any.worker.html?h264_annexb imported/w3c/web-platform-tests/webcodecs/videoDecoder-codec-specific.https.any.worker.html?h264_annexb