LibWeb: Add and implement CSSPropertyRule IDL and bindings

Author: https://github.com/a-ungurianu 🔰
Commit: 50d64b0fb7
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1777
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/AtkinsSJ ✅

Userland/Libraries/LibWeb/CSS/CSSRule.h

@@ -35,6 +35,7 @@ public:
         LayerBlock = 100,
         LayerStatement = 101,
         NestedDeclarations = 102,
+        Property = 103, // FIXME: This should return `0` as a type, but type is used for a lot of dispatching
     };
 
     virtual Type type() const = 0;