Fix `DatePicker` uses incorrect overlay color from `DatePickerTheme` and add missing tests (#130584)

fixes [YearPickerState in calendar_date_picker is using dayOverlayColor instead of yearOverlayColor](https://github.com/flutter/flutter/issues/130051)

### Description

- Fix year selection uses incorrect overlay color from `DatePickerTheme`
- Update defaults tests to check for overlay color for different modes
- Add tests to check overlay color is resolved.

### Code sample

<details> 
<summary>expand to view the 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(
      theme: ThemeData(
        datePickerTheme: const DatePickerThemeData(
          yearOverlayColor: MaterialStatePropertyAll<Color>(Colors.green),
          dayOverlayColor: MaterialStatePropertyAll<Color>(Colors.amber),
        ),
        useMaterial3: true,
      ),
      home: Directionality(
        textDirection: TextDirection.ltr,
        child: Material(
          child: Center(
            child: DatePickerDialog(
              initialDate: DateTime(2023, DateTime.january, 25),
              firstDate: DateTime(2022),
              lastDate: DateTime(2024, DateTime.december, 31),
              currentDate: DateTime(2023, DateTime.january, 24),
            ),
          ),
        ),
      ),
    );
  }
}

``` 
	
</details>

```dart
          yearOverlayColor: MaterialStatePropertyAll<Color>(Colors.green),
          dayOverlayColor: MaterialStatePropertyAll<Color>(Colors.red),
```

### Before
![Screenshot 2023-07-14 at 18 39 51](https://github.com/flutter/flutter/assets/48603081/52ec5096-bad6-4753-9e9a-15b6d5ce767e)

### After
![Screenshot 2023-07-14 at 18 38 32](https://github.com/flutter/flutter/assets/48603081/a51aeca8-a5c2-42b4-8c05-b55f9955e860)