CalendarDatePicker doesn't announce selected date on desktop (#143583)
fixes [Screen reader is not announcing the selected date as selected on DatePicker](https://github.com/flutter/flutter/issues/143439)
### Descriptions
- This fixes an issue where `CalendarDatePicker` doesn't announce selected date on desktop.
- Add semantic label to describe the selected date is indeed "Selected".
### Code sample
<details>
<summary>expand to view the code sample</summary>
```dart
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return const MaterialApp(
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({super.key, required this.title});
final String title;
@override
MyHomePageState createState() => MyHomePageState();
}
class MyHomePageState extends State<MyHomePage> {
void _showDatePicker() async {
await showDatePicker(
context: context,
initialDate: DateTime.now(),
firstDate: DateTime(1900),
lastDate: DateTime(2200),
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title,
style: const TextStyle(fontFamily: 'ProductSans')),
),
body: const Center(
child: Text('Click the button to show date picker.'),
),
floatingActionButton: FloatingActionButton(
onPressed: _showDatePicker,
tooltip: 'Show date picker',
child: const Icon(Icons.edit_calendar),
),
);
}
}
// import 'package:flutter/material.dart';
// void main() => runApp(const MyApp());
// class MyApp extends StatelessWidget {
// const MyApp({super.key});
// @override
// Widget build(BuildContext context) {
// return MaterialApp(
// debugShowCheckedModeBanner: false,
// home: Scaffold(
// body: Center(
// child: CalendarDatePicker(
// initialDate: DateTime.now(),
// firstDate: DateTime(2020),
// lastDate: DateTime(2050),
// onDateChanged: (date) {
// print(date);
// },
// ),
// ),
// ),
// );
// }
// }
```
</details>
### Before
https://github.com/flutter/flutter/assets/48603081/c82e1f15-f067-4865-8a5a-1f3c0c8d91da
### After
https://github.com/flutter/flutter/assets/48603081/193d9e26-df9e-4d89-97ce-265c3d564607
5d2353c105