LibWeb: Don't mark LiveNodeList as final

This is to accommodate for adding the RadioNodeList interface which
returns a live list of elements.

Userland/Libraries/LibWeb/DOM/LiveNodeList.h

@@ -14,7 +14,7 @@ namespace Web::DOM {
 
 // FIXME: Just like HTMLCollection, LiveNodeList currently does no caching.
 
-class LiveNodeList final : public NodeList {
+class LiveNodeList : public NodeList {
     WEB_PLATFORM_OBJECT(LiveNodeList, NodeList);
 
 public:
@@ -31,9 +31,10 @@ public:
 
     virtual bool is_supported_property_index(u32) const override;
 
-private:
+protected:
     LiveNodeList(JS::Realm&, Node& root, Scope, Function<bool(Node const&)> filter);
 
+private:
     virtual void visit_edges(Cell::Visitor&) override;
 
     JS::MarkedVector<Node*> collection() const;