LibJS+LibWeb: Use new Cell::Visitor helpers to avoid manual iteration

Author: https://github.com/awesomekling
Commit: 53d0dd4a2e
Pull-request: https://github.com/SerenityOS/serenity/pull/23971
Reviewed-by: https://github.com/trflynn89

Userland/Libraries/LibWeb/DOM/Node.cpp

@@ -106,8 +106,7 @@ void Node::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_paintable);
 
     if (m_registered_observer_list) {
-        for (auto& registered_observer : *m_registered_observer_list)
-            visitor.visit(registered_observer);
+        visitor.visit(*m_registered_observer_list);
     }
 }