[Cocoa] Adopt -[AVSampleBufferDisplayLayer readyForDisplay]
<rdar://problem/114112149>
Pull request: https://github.com/WebKit/WebKit/pull/19992
Committed 270234@main (671b61720416): <https://commits.webkit.org/270234@main> Reviewed commits have been landed. Closing PR #19992 and removing active labels.