LibWeb: Move setting of Web object prototypes to initialize()

This needs to happen before prototype/constructor intitialization can be
made lazy. Otherwise, GC could run during the C++ constructor and try to
collect the object currently being created.

Userland/Libraries/LibWeb/HTML/HTMLMenuElement.h

@@ -22,6 +22,8 @@ public:
 
 private:
     HTMLMenuElement(DOM::Document&, DOM::QualifiedName);
+
+    virtual void initialize(JS::Realm&) override;
 };
 
 }