LibJS: Move native objects towards two-pass construction

To make sure that everything is set up correctly in objects before we
start adding properties to them, we split cell allocation into 3 steps:

1. Allocate a cell of appropriate size from the Heap
2. Call the C++ constructor on the cell
3. Call initialize() on the constructed object

The job of initialize() is to define all the initial properties.
Doing it in a second pass guarantees that the Object has a valid Shape
and can find its own GlobalObject.

Libraries/LibJS/Runtime/Date.cpp

@@ -34,7 +34,7 @@ namespace JS {
 
 Date* Date::create(GlobalObject& global_object, Core::DateTime datetime, u16 milliseconds)
 {
-    return global_object.heap().allocate<Date>(datetime, milliseconds, *global_object.date_prototype());
+    return global_object.heap().allocate<Date>(global_object, datetime, milliseconds, *global_object.date_prototype());
 }
 
 Date::Date(Core::DateTime datetime, u16 milliseconds, Object& prototype)