Use dav1d decoder instead of libaom decoder
<rdar://problem/102804765>
Pull request: https://github.com/WebKit/WebKit/pull/6965
Committed 257283@main (111902f17da1): <https://commits.webkit.org/257283@main> Reviewed commits have been landed. Closing PR #6965 and removing active labels.
Reverted by https://github.com/WebKit/WebKit/pull/7073
Committed 257287@main (7a2231c029fc): <https://commits.webkit.org/257287@main> Reviewed commits have been landed. Closing PR #7073 and removing active labels.
Re-opening for pull request https://github.com/WebKit/WebKit/pull/7136
Committed 257357@main (61a22089e97a): <https://commits.webkit.org/257357@main> Reviewed commits have been landed. Closing PR #7136 and removing active labels.