fixes [MenuItemButton does not constrain its child](https://github.com/flutter/flutter/issues/129439)
fixes [DropdownMenuEntry Text Overflow when width of DropdownMenu is not specified](https://github.com/flutter/flutter/issues/140596)
### Description
- This PR continues the fix from https://github.com/flutter/flutter/pull/141314#issuecomment-1945804640 and adds controlled widths for the `MenuBar` children to fix the unbounded width issue which blocked the PR earlier. (Widgets with non-zero flex value cannot be laid out in a horizontal scroll view which is created by `MenuBar` widget)
- Added tests coverage.
- Added documentation.
### 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 StatefulWidget {
const MyApp({super.key});
@override
State<MyApp> createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
MenuController menuController = MenuController();
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Padding(
padding: const EdgeInsets.all(16.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
DropdownMenu<int>(
expandedInsets: EdgeInsets.zero,
dropdownMenuEntries: <DropdownMenuEntry<int>>[
DropdownMenuEntry<int>(
value: 0,
label:
'This is a long text that is multiplied by 10. ' * 10,
style: const ButtonStyle(
textStyle: MaterialStatePropertyAll(
TextStyle(overflow: TextOverflow.ellipsis),
),
),
),
],
),
SizedBox(
width: 200,
child: MenuItemButton(
onPressed: () {},
leadingIcon: const Icon(Icons.menu),
trailingIcon: const Icon(Icons.arrow_forward_ios),
child: const Text(
'This is a very long text that will wrap to the multiple lines.',
maxLines: 1,
overflow: TextOverflow.ellipsis,
),
),
),
// MenuBar(
// children: [
// MenuItemButton(
// onPressed: () {
// },
// child: Text('Short Text Menu'),
// ),
// MenuItemButton(
// onPressed: () {},
// child: Text('Very very very very very long text menu'),
// ),
// ],
// ),
],
),
),
),
);
}
}
```
</details>
### Before
### After
8d9dcc48ec