Fix wide DatePicker input mode button padding for Material 3 (#147236)
fixes [Wide `DatePickerDialog` "Switch to input" button has no margin from dialog side](https://github.com/flutter/flutter/issues/141338)
### Description
Currently, there is no material design token for the input mode button padding. This PR fixes the padding by taking date picker side padding values into account.
### 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 MaterialApp(
home: Scaffold(
body: Center(
child: Builder(builder: (BuildContext context) {
return ElevatedButton(
onPressed: () {
showDatePicker(
context: context,
initialDate: DateTime.now(),
firstDate: DateTime.utc(2010),
lastDate: DateTime.utc(2030),
);
},
child: const Text('Show Date Picker'),
);
}),
),
),
);
}
}
```
</details>
### Before
### After
7ff31a4f7a