Fixes #128696 (Motion checkbox)

This PR updates the Material 3 tab indicator animation, so that it stretches, as it can be seen in the showcase videos in the specification https://m3.material.io/components/tabs/accessibility#13ed756b-fb35-4bb3-ac8c-1157e49031d8

One thing to note is that the Material 3 videos have a tab transition duration of 700 ms, whereas currently in Flutter the duration is 300 ms. I recorded 4 comparison videos to see the difference better (current animation vs stretch animation  and  300 ms vs 700 ms)
@Piinks You mentioned the other day that the default tab size could be updated in the future to better reflect the new size in M3. Maybe the `kTabScrollDuration` constant is another one that could end up being updated, as 300 ms for this animation feels too fast.

Here are the comparison videos (Material 3 spec showcase on the left and Flutter on the right)

## Original animation - 300 ms

https://github.com/flutter/flutter/assets/22084723/d5b594fd-52ea-4328-b8e2-ddb597c81f69

## New animation - 300 ms

https://github.com/flutter/flutter/assets/22084723/c822f7ab-3fc4-4403-a53b-872d047f6227

---

## Original animation - 700 ms

https://github.com/flutter/flutter/assets/22084723/fe39a32d-3d10-4c0d-98df-bd5e1c9336d0

## New animation - 700 ms

https://github.com/flutter/flutter/assets/22084723/8d4b0628-6312-40c2-bd99-b4bcb8e23ba9

---

## Code sample

```dart
void main() => runApp(const MyApp());

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      home: TabExample(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      initialIndex: 1,
      length: 3,
      child: Scaffold(
        appBar: AppBar(
          title: const Text('My saved media'),
          bottom: const TabBar(
            tabs: <Widget>[
              Tab(
                icon: Icon(Icons.videocam_outlined),
                text: "Video",
              ),
              Tab(
                icon: Icon(Icons.photo_outlined),
                text: "Photos",
              ),
              Tab(
                icon: Icon(Icons.audiotrack),
                text: "Audio",
              ),
            ],
          ),
        ),
        body: const TabBarView(
          children: <Widget>[
            Center(
              child: Text("Tab 1"),
            ),
            Center(
              child: Text("Tab 2"),
            ),
            Center(
              child: Text("Tab 3"),
            ),
          ],
        ),
      ),
    );
  }
}
```

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*