style: Implement color() function from CSS specification

Colors can now be defined in different color spaces with the color()
function.

https://w3c.github.io/csswg-drafts/css-color-4/#predefined

Differential Revision: https://phabricator.services.mozilla.com/D164866

components/style/lib.rs

@@ -80,6 +80,7 @@ pub mod attr;
 pub mod author_styles;
 pub mod bezier;
 pub mod bloom;
+pub mod color;
 #[path = "properties/computed_value_flags.rs"]
 pub mod computed_value_flags;
 pub mod context;