Fix TabBarTheme.indicatorColor not applied in Material 2 (#132123)
fixes [[Proposal] Improve TabBarTheme styling API for indicator color ](https://github.com/flutter/flutter/issues/130392)
### Description
This fixes an issue where the `TabBarTheme.indicator` isn't applied in Material 2 and also adds indicator color tests for both M3 and M2.
### Code sample
<details>
<summary>expand to view the code sample</summary>
```dart
import 'package:flutter/material.dart';
/// Flutter code sample for [TabBar].
void main() => runApp(const TabBarApp());
class TabBarApp extends StatelessWidget {
const TabBarApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(
useMaterial3: false,
tabBarTheme: const TabBarTheme(
indicatorColor: Colors.amber,
)
),
home: const TabBarExample(),
);
}
}
class TabBarExample extends StatelessWidget {
const TabBarExample({super.key});
@override
Widget build(BuildContext context) {
return DefaultTabController(
initialIndex: 1,
length: 3,
child: Scaffold(
appBar: AppBar(
title: const Text('TabBar Sample'),
bottom: const TabBar(
tabs: <Widget>[
Tab(
icon: Icon(Icons.cloud_outlined),
text: 'Cloudy',
),
Tab(
icon: Icon(Icons.beach_access_sharp),
text: 'Sunny',
),
Tab(
icon: Icon(Icons.brightness_5_sharp),
text: 'Rainy',
),
],
),
),
body: const TabBarView(
children: <Widget>[
Center(
child: Text("It's cloudy here"),
),
Center(
child: Text("It's rainy here"),
),
Center(
child: Text("It's sunny here"),
),
],
),
),
);
}
}
```
</details>
### Before
### After
ee47267d26