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/HTMLInputElement.h

@@ -134,6 +134,7 @@ private:
     // ^DOM::Element
     virtual i32 default_tab_index_value() const override;
 
+    virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
     static TypeAttributeState parse_type_attribute(StringView);