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/CSSPropertyRule.idl

@@ -0,0 +1,11 @@
+#import <CSS/CSSRule.idl>
+
+// https://drafts.css-houdini.org/css-properties-values-api/#the-css-property-rule-interface
+[Exposed=Window]
+interface CSSPropertyRule : CSSRule {
+    readonly attribute CSSOMString name;
+    readonly attribute CSSOMString syntax;
+    readonly attribute boolean inherits;
+    readonly attribute CSSOMString? initialValue;
+
+};