[scroll-anchoring] Exclude absolutely positioned elements with containing blocks outside the parent scroller
<rdar://problem/116201738>
Pull request: https://github.com/WebKit/WebKit/pull/18379
Committed 270551@main (c3a46a009b28): <https://commits.webkit.org/270551@main> Reviewed commits have been landed. Closing PR #18379 and removing active labels.