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.cpp

@@ -81,6 +81,7 @@ FlyString const& CSSRule::parent_layer_internal_qualified_name_slow_case() const
         case Type::Namespace:
         case Type::Supports:
         case Type::NestedDeclarations:
+        case Type::Property:
             break;
         }
     }