fonts: Add support for more @font-face features (#32164)

There are a couple major changes here:

1. Support is added for the `weight`, `style`, `stretch` and
   `unicode-range` declarations in `@font-face`.
2. Font matching in the font cache can return templates and
   `FontGroupFamily` can own mulitple templates. This is due to needing
   support for "composite fonts". These are `@font-face` declarations
   that only differ in their `unicode-range` definition.

This fixes a lot of non-determinism in font selection especially when
dealing with pages that define "composite faces." A notable example of
such a page is servo.org, which now consistently displays the correct
web font.

One test starts to fail due to an uncovered bug, but this will be fixed
in a followup change.

Fixes #20686.
Fixes #20684.

Co-authored-by: Mukilan Thiyagarajan <mukilan@igalia.com>

components/gfx/platform/windows/font.rs

@@ -186,11 +186,7 @@ impl PlatformFontMethods for PlatformFont {
             StyleFontStyle::NORMAL
         };
 
-        FontTemplateDescriptor {
-            weight,
-            stretch,
-            style,
-        }
+        FontTemplateDescriptor::new(weight, stretch, style)
     }
 
     fn glyph_index(&self, codepoint: char) -> Option<GlyphId> {