Implement font-language-override

[shivamidow]

409efd5ab32743edb9eec26883621e3044f23486

Implement font-language-override
https://bugs.webkit.org/show_bug.cgi?id=150081

Reviewed by NOBODY (OOPS!).

WIP.

* Source/WebCore/css/CSSProperties.json:
* Source/WebCore/css/ComputedStyleExtractor.cpp:
(WebCore::ComputedStyleExtractor::valueForPropertyInStyle):
* Source/WebCore/platform/graphics/FontCascadeDescription.cpp:
* Source/WebCore/platform/graphics/FontCascadeDescription.h:
(WebCore::FontCascadeDescription::initialLanguageOverride):
* Source/WebCore/platform/graphics/FontDescription.cpp:
(WebCore::FontDescription::setLanguageOverride):
* Source/WebCore/platform/graphics/FontDescription.h:
(WebCore::FontDescription::languageOverride const):
* Source/WebCore/rendering/style/RenderStyle.h:
* Source/WebCore/rendering/style/RenderStyleInlines.h:
(WebCore::RenderStyle::fontLanguageOverride const):
* Source/WebCore/style/StyleBuilderCustom.h:
(WebCore::Style::BuilderCustom::applyValueFontLanguageOverride):

bf590eb

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
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash 409efd5)

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
	✅ 🛠 watch
	✅ 🛠 watch-sim

[litherum]

Is this a good idea?

I've spoken in the CSSWG about how I think this property shouldn't exist, and authors should just use lang= instead.

[shivamidow]

Hi @litherum, thanks for your interest in this WIP patch. I just aimed to see how font-language-override is compatible with the existing local implementation, but thanks for your comment anyway.

I am aware of w3c/csswg-drafts#5484. My rationale and motivation for this feature are three.

1. Gecko has supported it. And there is a strong objection to dropping this feature from the spec. So, it would be good if WebKit also supports font-language-override for interoperability.
2. As explained in the ticket in the CSS working group, the language locale and font-size-adjust have slightly different purposes and functionalities. In my understanding, font-size-adjust not only sets language but also affects glyph rendering. It gives web designers more control.
3. WebKit already supports a non-standard language designation CSS property, --webkit-locale. I think it would be better if we can replace it with a standard one, --font-language-override.

We can continue our discussion in the ticket of the CSS WG.

[webkit-early-warning-system]

EWS run on current version of this PR (hash bf590eb)

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
	✅ 🛠 watch
	✅ 🛠 watch-sim