IntersectionObserver should not notify targets in detached documents

[Ahmad-S792]

b49b5a0

IntersectionObserver should not notify targets in detached documents
https://bugs.webkit.org/show_bug.cgi?id=300729
rdar://162699098

Reviewed by Chris Dumez.

HTML's "update the rendering" steps build the docs list from "all
fully active Document objects" [1], so the intersection observer
update step (Step 19) [1] never runs for a detached document. A
target whose owning Document is not fully active therefore cannot
legitimately produce an intersection.

WebKit still queued an initial zero-rect, not-intersecting entry for
such targets, so target-in-detached-document.html saw one notification
before the target was adopted into a fully-active document where the
specification expect none.

Fix it by skipping such targets in updateObservations without
advancing previousThresholdIndex, so a later adoptNode is treated as
the first observation.

This skip is gated on implicit root observers, "Update the rendering"
[1] (Step 19) invoke "run the update intersection observations
steps" [2] which iterates "all IntersectionObservers whose root is
in the DOM tree of document … this includes implicit root
observers". The explicit-root [3] case is left alone and continues
to be tested by explicit-root-different-document.html.

Drop the skipped target from m_targetsWaitingForFirstObservation so a
permanently detached target/document can be collected
(i.e., intersection-observer/no-document-leak.html).

[1] https://html.spec.whatwg.org/#update-the-rendering
[2] https://w3c.github.io/IntersectionObserver/#run-the-update-intersection-observations-steps
[3] https://w3c.github.io/IntersectionObserver/#intersectionobserver-explicit-root-observer

* LayoutTests/imported/w3c/web-platform-tests/intersection-observer/target-in-detached-document-expected.txt: Progression
* Source/WebCore/page/IntersectionObserver.cpp:
(WebCore::IntersectionObserver::updateObservations):

Canonical link: https://commits.webkit.org/313834@main

c84a26e

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	✅ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	❌ 🧪 win-tests	✅ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		✅ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim	✅ 🧪 mac-site-isolation
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash f800c2c)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	🛠 ios	✅ 🛠 mac	🛠 wpe	✅ 🛠 win	✅ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2	❌ 🧪 win-tests	✅ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	🧪 api-wpe		✅ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	🧪 mac-wk2	✅ 🧪 gtk-wk2
	🛠 vision	🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	❌ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim	🧪 mac-site-isolation
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash c84a26e)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	✅ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	❌ 🧪 win-tests	✅ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		✅ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim	✅ 🧪 mac-site-isolation
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 313834@main (b49b5a0): https://commits.webkit.org/313834@main

Reviewed commits have been landed. Closing PR #65550 and removing active labels.