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/HTMLFormElement.h

@@ -43,6 +43,7 @@ public:
 private:
     HTMLFormElement(DOM::Document&, DOM::QualifiedName);
 
+    virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
     bool m_firing_submission_events { false };