flutter/flutter@67457e6...4145645

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-stable-packages
Please CC [email protected],[email protected],[email protected] on the revert to ensure that a human
is aware of the problem.

To file a bug in Flutter (stable): https://github.com/flutter/flutter/issues/new/choose
To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

I never updated the contributing notes about languages when we added
Kotlin to the repo.

This PR exposes the current top route to `GoRouterState`, this allows `ShellRoute` to know what is the current child and process the state accordingly.

- Issue: flutter/flutter#140297

This could be used like this, given that each `GoRoute` had the `name` parameter given
```dart
StatefulShellRoute.indexedStack(
  parentNavigatorKey: rootNavigatorKey,
  builder: (
    BuildContext context,
    GoRouterState state,
    StatefulNavigationShell navigationShell,
  ) {
    final String? routeName =
        GoRouterState.of(context).topRoute.name;
    final String title = switch (routeName) {
      'a' => 'A',
      'b' => 'B',
      _ => 'Unknown',
    };
    return Column(
      children: <Widget>[
        Text(title),
        Expanded(child: navigationShell),
      ],
    );
  },
  ...
}
```

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