LibJS: Move intrinsics to the realm

Intrinsics, i.e. mostly constructor and prototype objects, but also
things like empty and new object shape now live on a new heap-allocated
JS::Intrinsics object, thus completing the long journey of taking all
the magic away from the global object.
This represents the Realm's [[Intrinsics]] slot in the spec and matches
its existing [[GlobalObject]] / [[GlobalEnv]] slots in terms of
architecture.

In the majority of cases it should now be possibly to fully allocate a
regular object without the global object existing, and in fact that's
what we do now - the realm is allocated before the global object, and
the intrinsics between both :^)

Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp

@@ -11,7 +11,7 @@
 namespace JS {
 
 ModuleNamespaceObject::ModuleNamespaceObject(Realm& realm, Module* module, Vector<FlyString> exports)
-    : Object(*realm.global_object().object_prototype())
+    : Object(*realm.intrinsics().object_prototype())
     , m_module(module)
     , m_exports(move(exports))
 {