Update ImageBuffer to subclass ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr.
Pull request: https://github.com/WebKit/WebKit/pull/16418
Committed 266637@main (32c4cca3e762): <https://commits.webkit.org/266637@main> Reviewed commits have been landed. Closing PR #16418 and removing active labels.
<rdar://problem/113503988>