[Cupertino] Add Action Sheet & Dialog

Author: IIzzaya

Runtime/cupertino/action_sheet.cs

@@ -124,7 +124,13 @@ void _updateNavigator() {
                 this._navigatorObservers = new List<NavigatorObserver>();
             }
         }
-
+        
+        // Iterable<LocalizationsDelegate<dynamic>> get _localizationsDelegates sync* {
+        //     if (widget.localizationsDelegates != null)
+        //         yield* widget.localizationsDelegates;
+        //     yield DefaultCupertinoLocalizations.delegate; 
+        // }
+        
         List<LocalizationsDelegate> _localizationsDelegates {
             get {
                 List<LocalizationsDelegate<CupertinoLocalizations>> _delegates =