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/Heap/Heap.h

@@ -46,13 +46,23 @@ public:
     ~Heap();
 
     template<typename T, typename... Args>
-    T* allocate(Args&&... args)
+    T* allocate_without_global_object(Args&&... args)
     {
         auto* memory = allocate_cell(sizeof(T));
         new (memory) T(forward<Args>(args)...);
         return static_cast<T*>(memory);
     }
 
+    template<typename T, typename... Args>
+    T* allocate(GlobalObject& global_object, Args&&... args)
+    {
+        auto* memory = allocate_cell(sizeof(T));
+        new (memory) T(forward<Args>(args)...);
+        auto* cell = static_cast<T*>(memory);
+        cell->initialize(m_interpreter, global_object);
+        return cell;
+    }
+
     enum class CollectionType {
         CollectGarbage,
         CollectEverything,