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/NumberConstructor.cpp

@@ -37,8 +37,12 @@
 
 namespace JS {
 
-NumberConstructor::NumberConstructor()
-    : NativeFunction("Number", *interpreter().global_object().function_prototype())
+NumberConstructor::NumberConstructor(GlobalObject& global_object)
+    : NativeFunction("Number", *global_object.function_prototype())
+{
+}
+
+void NumberConstructor::initialize(Interpreter&, GlobalObject&)
 {
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function("isFinite", is_finite, 1, attr);