fixes https://github.com/flutter/flutter/issues/114340

<details> 
<summary>code sample</summary> 

```dart
import 'package:flutter/material.dart';

/// Flutter code sample for [SliverAppBar.medium].

void main() {
  runApp(const AppBarMediumApp());
}

class AppBarMediumApp extends StatelessWidget {
  const AppBarMediumApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        useMaterial3: true,
      ),
      home: MediaQuery(
        data: MediaQuery.of(context).copyWith(textScaleFactor: 3.0),
        child: Material(
          child: CustomScrollView(
            slivers: <Widget>[
              SliverAppBar.medium(
                leading:
                    IconButton(icon: const Icon(Icons.menu), onPressed: () {}),
                title: const Text('Medium App Bar'),
                actions: <Widget>[
                  IconButton(icon: const Icon(Icons.more_vert), onPressed: () {}),
                ],
              ),
              // SliverAppBar.large(
              //   leading:
              //       IconButton(icon: const Icon(Icons.menu), onPressed: () {}),
              //   title: const Text('Large App Bar'),
              //   actions: <Widget>[
              //     IconButton(
              //         icon: const Icon(Icons.more_vert), onPressed: () {}),
              //   ],
              // ),
              // Just some content big enough to have something to scroll.
              SliverToBoxAdapter(
                child: Card(
                  child: SizedBox(
                    height: 1200,
                    child: Padding(
                      padding: const EdgeInsets.fromLTRB(8, 100, 8, 100),
                      child: Text(
                        'Here be scrolling content...',
                        style: Theme.of(context).textTheme.headlineSmall,
                      ),
                    ),
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

``` 
	
</details>

### Before
|  Medium App Bar - `textScaleFactor: 3.0` |   Large App Bar - `textScaleFactor.30` |
| --------------- | --------------- |
| <img src="https://user-images.githubusercontent.com/48603081/232815191-ab42523b-d710-4c93-a889-e9c92ca472c8.png" height="450" /> | <img src="https://user-images.githubusercontent.com/48603081/232815232-104c208d-f1dd-404e-9218-5dfb61244d56.png" height="450" /> |

### After
|  Medium App Bar - `textScaleFactor: 3.0` |   Large App Bar - `textScaleFactor.30` |
| --------------- | --------------- |
| <img src="https://user-images.githubusercontent.com/48603081/232815733-8b8af94f-197f-427a-bbb9-bc6cd0173658.png" height="450" /> | <img src="https://user-images.githubusercontent.com/48603081/232815758-2c336d14-085b-4e91-8b93-748a40822ea6.png" height="450" /> |