Adopt ThreadSafeWeakPtr in LocalSampleBufferDisplayLayer
<rdar://problem/111203259>
Pull request: https://github.com/WebKit/WebKit/pull/15230
Committed 265461@main (0a7b2cd6eaaf): <https://commits.webkit.org/265461@main> Reviewed commits have been landed. Closing PR #15230 and removing active labels.