LibWeb: Make CSSStyleDeclaration GC-allocated

Author: https://github.com/awesomekling
Commit: 72bacba97b
Pull-request: https://github.com/SerenityOS/serenity/pull/14816
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibWeb/CSS/CSSStyleDeclaration.idl

@@ -1,4 +1,4 @@
-[CustomGet,CustomSet,CustomHasProperty]
+[NoInstanceWrapper]
 interface CSSStyleDeclaration {
 
     readonly attribute unsigned long length;