[CSS Nesting] Don't serialize first implicit style rule inside group rule

[mdubet]

e07871e

[CSS Nesting] Don't serialize first implicit style rule inside group rule
https://bugs.webkit.org/show_bug.cgi?id=256647
rdar://109208359

Reviewed by Antti Koivisto.

Orphaned properties in group rule are implicitly added
to a style rule with '&' as selector ;
this implicit style rule should not be serialized.

* LayoutTests/imported/w3c/web-platform-tests/css/css-nesting/parsing-expected.txt:
* LayoutTests/imported/w3c/web-platform-tests/css/css-nesting/parsing.html:
* LayoutTests/imported/w3c/web-platform-tests/css/css-nesting/serialize-group-rules-with-decls.tentative-expected.txt:
* LayoutTests/imported/w3c/web-platform-tests/css/css-nesting/serialize-group-rules-with-decls.tentative.html:

 Import from WPT

* Source/WebCore/css/CSSGroupingRule.cpp:
(WebCore::CSSGroupingRule::appendCSSTextForItems const):
(WebCore::CSSGroupingRule::cssTextForDeclsAndRules const):
* Source/WebCore/css/CSSStyleRule.cpp:
(WebCore::CSSStyleRule::cssTextForDeclsAndRules const):

This behavior only concerns group rule, not style rule (where a property can't be orphaned)

Canonical link: https://commits.webkit.org/264003@main

5c8e400

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash e355a61)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	🧪 ios-wk2-wpt	🧪 mac-wk1	⏳ 🧪 gtk-wk2
	✅ 🧪 api-ios	🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim	❌ 🧪 mac-wk2-stress
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash 5c8e400)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 264003@main (e07871e): https://commits.webkit.org/264003@main

Reviewed commits have been landed. Closing PR #13758 and removing active labels.