fixes [`DatePickerDialog` date entry hover background and ink splash have different radius](https://github.com/flutter/flutter/issues/141350)
fixes [Ability to customize DatePicker day selection background and overlay shape](https://github.com/flutter/flutter/issues/144220)

### 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(
      home: Scaffold(
        body: Center(
          child: Builder(builder: (context) {
            return FilledButton(
              onPressed: () {
                showDatePicker(
                  context: context,
                  initialDate: DateTime.now(),
                  firstDate: DateTime.utc(2010),
                  lastDate: DateTime.utc(2030),
                );
              },
              child: const Text('Show Date picker'),
            );
          }),
        ),
      ),
    );
  }
}
```

</details>

### Material DatePicker states specs

![overlay_specs](https://github.com/flutter/flutter/assets/48603081/45ce16cf-7ee9-41e1-a4fa-327de07b78d1)

### Day selection overlay

| Before | After |
| --------------- | --------------- |
| <img src="https://github.com/flutter/flutter/assets/48603081/b529d38d-0232-494b-8bf2-55d28420a245" /> | <img src="https://github.com/flutter/flutter/assets/48603081/c4799559-a7ef-45fd-aed9-aeb386370580"  /> |

### Hover, pressed, highlight preview

| Before | After |
| --------------- | --------------- |
| <video src="https://github.com/flutter/flutter/assets/48603081/8edde82a-7f39-4482-afab-183e1bce5991" /> | <video src="https://github.com/flutter/flutter/assets/48603081/04e1502e-67a4-4b33-973d-463067d70151" /> |

### Using `DatePickerThemeData.dayShape` to customize day selection background and overlay shape

| Before | After |
| --------------- | --------------- |
| <img src="https://github.com/flutter/flutter/assets/48603081/a0c85f58-a69b-4e14-a45d-41e580ceedce"  />  | <img src="https://github.com/flutter/flutter/assets/48603081/db67cee1-d28d-4168-98b8-fd7a9cb70cda" /> | 

### Example preview

![Screenshot 2024-02-29 at 15 07 50](https://github.com/flutter/flutter/assets/48603081/3770ed5c-28bf-4d0a-9514-87e1cd2ce515)