LibWeb: Implement (most of) NamedNodeMap to store attributes

Author: https://github.com/trflynn89
Commit: 2a3ac02ef1
Pull-request: https://github.com/SerenityOS/serenity/pull/10510
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/Forward.h

@@ -88,6 +88,7 @@ class EventListener;
 class EventTarget;
 class HTMLCollection;
 class LiveNodeList;
+class NamedNodeMap;
 class Node;
 class NodeList;
 class ParentNode;
@@ -400,6 +401,7 @@ class MessageChannelWrapper;
 class MessageEventWrapper;
 class MessagePortWrapper;
 class MouseEventWrapper;
+class NamedNodeMapWrapper;
 class NodeListWrapper;
 class NodeWrapper;
 class PageTransitionEventWrapper;