Fix showBottomSheet doesn't remove scrim when draggable sheet is dismissed (#128455)
fixes https://github.com/flutter/flutter/issues/128367
<details>
<summary>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(
debugShowCheckedModeBanner: false,
theme: ThemeData(useMaterial3: true),
home: Scaffold(
floatingActionButton: Builder(
builder: (BuildContext context) => FloatingActionButton(
child: const Icon(Icons.add),
onPressed: () {
Scaffold.of(context).showBottomSheet<void>(
(_) {
return DraggableScrollableSheet(
expand: false,
builder: (_, ScrollController scrollController) =>
ListView.builder(
controller: scrollController,
itemCount: 25,
itemBuilder: (BuildContext context, int index) {
return ListTile(
title: Text('Item $index - tap to close'),
onTap: () {
Navigator.of(context).pop();
},
);
},
),
);
},
);
},
),
),
),
);
}
}
```
</details>
### Before
https://github.com/flutter/flutter/assets/48603081/fa87feb9-54f2-4e50-bf71-c81d9e54ff61
### After
https://github.com/flutter/flutter/assets/48603081/7d192059-7600-4d65-ae84-6321f3598133
8600eb129c