[content-visibility] Support c-v for resize/intersection observer.
<rdar://problem/100802455>
Created attachment 463214 [details] Patch
Created attachment 463346 [details] Patch
Created attachment 463347 [details] Patch
Created attachment 463805 [details] Patch
Pull request: https://github.com/WebKit/WebKit/pull/6973
Committed 257256@main (56fda589ecc2): <https://commits.webkit.org/257256@main> Reviewed commits have been landed. Closing PR #6973 and removing active labels.