LibWeb: Implement the Element attributes getter

Author: https://github.com/trflynn89
Commit: 5d4cd061c7
Pull-request: https://github.com/SerenityOS/serenity/pull/10510
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/DOM/Element.h

@@ -56,6 +56,7 @@ public:
     ExceptionOr<void> set_attribute(const FlyString& name, const String& value);
     void remove_attribute(const FlyString& name);
     size_t attribute_list_size() const { return m_attributes->length(); }
+    NonnullRefPtr<NamedNodeMap> const& attributes() const { return m_attributes; }
 
     DOM::ExceptionOr<bool> matches(StringView selectors) const;