feat: add FormBuilderCupertinoDateTimePicker

Author: charlieforward9

example/lib/main.dart

@@ -100,7 +100,13 @@ class _MyHomePageState extends State<MyHomePage> {
                   autovalidateMode: AutovalidateMode.onUserInteraction,
                   validator: (value) =>
                       value != null && value.length > 4 ? null : 'Write a text',
-                )
+                ),
+                const SizedBox(height: 16),
+                FormBuilderCupertinoDateTimePicker(
+                  name: 'date',
+                  autovalidateMode: AutovalidateMode.onUserInteraction,
+                  validator: (value) => value != null ? null : 'Required date',
+                ),
               ],
             ),
           ),

lib/form_builder_cupertino_fields.dart

@@ -1,4 +1,5 @@
 export 'src/fields/form_builder_cupertino_checkbox.dart';
+export 'src/fields/form_builder_cupertino_datetime_picker.dart';
 export 'src/fields/form_builder_cupertino_segmented_control.dart';
 export 'src/fields/form_builder_cupertino_slider.dart';
 export 'src/fields/form_builder_cupertino_sliding_segmented_control.dart';