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

packages/flutter/lib/src/material/scaffold.dart

@@ -2312,6 +2312,8 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
 
       bottomSheetKey.currentState!.close();
       setState(() {
+        _showBodyScrim = false;
+        _bodyScrimColor = Colors.black.withOpacity(0.0);
         _currentBottomSheet = null;
       });
 

packages/flutter/test/material/scaffold_test.dart

@@ -2754,6 +2754,52 @@ void main() {
 
     expect(tester.takeException(), isNull);
   });
+
+  testWidgets('showBottomSheet removes scrim when draggable sheet is dismissed', (WidgetTester tester) async {
+    final DraggableScrollableController draggableController = DraggableScrollableController();
+    final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey();
+    PersistentBottomSheetController<void>? sheetController;
+
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        key: scaffoldKey,
+        body: const Center(child: Text('body')),
+      ),
+    ));
+
+    sheetController = scaffoldKey.currentState!.showBottomSheet<void>((_) {
+      return DraggableScrollableSheet(
+        expand: false,
+        controller: draggableController,
+        builder: (BuildContext context, ScrollController scrollController) {
+          return SingleChildScrollView(
+            controller: scrollController,
+            child: const Placeholder(),
+          );
+        },
+      );
+    });
+
+    Finder findModalBarrier() => find.descendant(of: find.byType(Scaffold), matching: find.byType(ModalBarrier));
+
+    await tester.pump();
+    expect(find.byType(BottomSheet), findsOneWidget);
+
+    // The scrim is not present yet.
+    expect(findModalBarrier(), findsNothing);
+
+    // Expand the sheet to 80% of parent height to show the scrim.
+    draggableController.jumpTo(0.8);
+    await tester.pump();
+    expect(findModalBarrier(), findsOneWidget);
+
+    // Dismiss the sheet.
+    sheetController.close();
+    await tester.pumpAndSettle();
+
+    // The scrim should be gone.
+    expect(findModalBarrier(), findsNothing);
+  });
 }
 
 class _GeometryListener extends StatefulWidget {