LibWeb: Support Element.closest(selectors)

Author: https://github.com/EdwinHoksberg
Commit: c646afc26c
Pull-request: https://github.com/SerenityOS/serenity/pull/12560
Reviewed-by: https://github.com/trflynn89 ✅

Userland/Libraries/LibWeb/DOM/Element.h

@@ -63,6 +63,7 @@ public:
     RefPtr<DOMTokenList> const& class_list();
 
     DOM::ExceptionOr<bool> matches(StringView selectors) const;
+    DOM::ExceptionOr<DOM::Element const*> closest(StringView selectors) const;
 
     int client_top() const;
     int client_left() const;