LibJS: Tweak Interpreter::create() for more spec-likeness

Store a reference to the newly created execution context in an aptly
named variable, rename global_this_value to just this_value, and only
call set_global_object() in a single place.

Userland/Libraries/LibJS/Interpreter.h

@@ -47,35 +47,36 @@ class Interpreter : public Weakable<Interpreter> {
  // 1. Let realm be CreateRealm().
  auto* realm = Realm::create(vm);
 
- // 2. Let newContext be a new execution context. (This was done in the Interpreter constructor)
+ // 2. Let newContext be a new execution context.
+ auto& new_context = interpreter->m_global_execution_context;
 
  // 3. Set the Function of newContext to null. (This is done for us when the execution context is constructed)
 
  // 4. Set the Realm of newContext to realm.
- interpreter->m_global_execution_context.realm = realm;
+ new_context.realm = realm;
 
  // 5. Set the ScriptOrModule of newContext to null. (This was done during execution context construction)
 
  // 6. Push newContext onto the execution context stack; newContext is now the running execution context.
- vm.push_execution_context(interpreter->m_global_execution_context);
+ vm.push_execution_context(new_context);
 
  // 7. If the host requires use of an exotic object to serve as realm's global object, let global be such an object created in a host-defined manner.
  // Otherwise, let global be undefined, indicating that an ordinary object should be created as the global object.
  auto* global_object = static_cast<GlobalObject*>(interpreter->heap().allocate_without_global_object<GlobalObjectType>(forward<Args>(args)...));
 
  // 8. If the host requires that the this binding in realm's global scope return an object other than the global object, let thisValue be such an object created
  // in a host-defined manner. Otherwise, let thisValue be undefined, indicating that realm's global this binding should be the global object.
+ Object* this_value;
  if constexpr (IsSame<GlobalObjectType, GlobalThisObjectType>) {
- // 9. Perform SetRealmGlobalObject(realm, global, thisValue).
- realm->set_global_object(*global_object, global_object);
+ this_value = global_object;
  } else {
  // FIXME: Should we pass args in here? Let's er on the side of caution and say yes.
- auto* global_this_value = static_cast<Object*>(interpreter->heap().allocate_without_global_object<GlobalThisObjectType>(forward<Args>(args)...));
-
- // 9. Perform SetRealmGlobalObject(realm, global, thisValue).
- realm->set_global_object(*global_object, global_this_value);
+ this_value = static_cast<Object*>(interpreter->heap().allocate_without_global_object<GlobalThisObjectType>(forward<Args>(args)...));
  }
 
+ // 9. Perform SetRealmGlobalObject(realm, global, thisValue).
+ realm->set_global_object(*global_object, this_value);
+
  // NOTE: These are not in the spec.
  static FlyString global_execution_context_name = "(global execution context)";
  interpreter->m_global_execution_context.function_name = global_execution_context_name;