typedef over Function for controller builders

- both GetX and GetBuilder
- now typesafe return instead of empty Function

@@ -6,8 +6,11 @@ import 'package:get_instance/get_instance.dart';
 import 'package:get_rx/get_rx.dart';
 import '../../get_state_manager.dart';
 
+typedef GetXControllerBuilder<T extends DisposableInterface> = Widget Function(
+    T controller);
+
 class GetX<T extends DisposableInterface> extends StatefulWidget {
-  final Widget Function(T) builder;
+  final GetXControllerBuilder<T> builder;
   final bool global;
 
   // final Stream Function(T) stream;

@@ -123,8 +123,11 @@ class GetxController extends DisposableInterface {
   /// }
 }
 
+typedef GetControllerBuilder<T extends DisposableInterface> = Widget Function(
+    T controller);
+
 class GetBuilder<T extends GetxController> extends StatefulWidget {
-  final Widget Function(T) builder;
+  final GetControllerBuilder<T> builder;
   final bool global;
   final String id;
   final String tag;