[css-anchor-position-1] Put position-visibility under a separate feature flag

[tuankiet65]

5cbd2c6

[css-anchor-position-1] Put position-visibility under a separate feature flag
rdar://150086754
https://bugs.webkit.org/show_bug.cgi?id=292090

Reviewed by Antti Koivisto.

Currently, all CSS anchor positioning features are behind an enabled-by-default
flag, CSSAnchorPositioningEnabled. However, position-visibility hasn't reached
feature complete yet (parsing is implemented but not layout implementation),
so put it under a separate, disabled-by-default flag.

* LayoutTests/fast/css/css-anchor-position/anchor-feature-disabled-expected.txt:
* LayoutTests/fast/css/css-anchor-position/anchor-feature-disabled.html:
    - Added tests to ensure position-visibility doesn't parse when the feature
      flag is disabled.

* Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml:
    - Added new feature flag for position-visibility.

* Source/WebCore/css/CSSProperties.json:
    - Changed position-visibility to use the new feature flag.

Canonical link: https://commits.webkit.org/294361@main

b356b95

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-cairo
✅ 🛠 🧪 jsc	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
✅ 🛠 🧪 jsc-arm64	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2	✅ 🛠 playstation
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp	✅ 🛠 jsc-armv7
	✅ 🛠 tv-sim		✅ 🧪 jsc-armv7-tests
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash b356b95)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-cairo
✅ 🛠 🧪 jsc	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
✅ 🛠 🧪 jsc-arm64	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2	✅ 🛠 playstation
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp	✅ 🛠 jsc-armv7
	✅ 🛠 tv-sim		✅ 🧪 jsc-armv7-tests
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 294361@main (5cbd2c6): https://commits.webkit.org/294361@main

Reviewed commits have been landed. Closing PR #44713 and removing active labels.