Repository: flutter
Issue: [pigeon] Support for default values in data classes
Labels: c: new feature,package,team-ecosystem,p: pigeon,P2,triaged-ecosystem

### Steps to reproduce

1. Use pigeon 22.7.2
2. Create pigeon file `pigeons/messages.dart ` containing:

```dart
@ConfigurePigeon(
  PigeonOptions(
    dartOut: 'lib/src/api.g.dart',
    kotlinOut:
        'android/src/main/kotlin/com/example/api/api/api.g.kt',
    swiftOut: 'ios/Classes/api.g.swift',
    kotlinOptions: KotlinOptions(package: 'com.example.api.api'),
  ),
)
class Something {
  final int number;

  Something({this.number = 5});
}
```
3. run `dart run pigeon --input pigeons/messages.dart `

According to closed [issue](https://github.com/flutter/flutter/issues/98448) and merged [pull-request](https://github.com/flutter/packages/pull/5355) (Adds default values for class constructors and host API methods.) it should work.

### Expected results

Dart output:
```dart
class Something {
  Something({
    this.number = 5,
  });

  int number;

  Object encode() {
    return <Object?>[
      number,
    ];
  }

  static Something decode(Object result) {
    result as List<Object?>;
    return Something(
      number: result[0]! as int,
    );
  }
}
```

Swift output:

```swift
struct Something {
  var number: Int64 = 5


  // swift-format-ignore: AlwaysUseLowerCamelCase
  static func fromList(_ pigeonVar_list: [Any?]) -> Something? {
    let number = pigeonVar_list[0] as! Int64

    return Something(
      number: number
    )
  }
  func toList() -> [Any?] {
    return [
      number
    ]
  }
}
```

Kotlin output:

```kotlin
data class Something(
  val number: Long = 5
) {
  companion object {
    fun fromList(pigeonVar_list: List<Any?>): Something {
      val number = pigeonVar_list[0] as Long
      return Something(number)
    }
  }
  fun toList(): List<Any?> {
    return listOf(
      number,
    )
  }
}

```

### Actual results

Dart output:
```dart
class Something {
  Something({
    required this.number,
  });

  int number;

  Object encode() {
    return <Object?>[
      number,
    ];
  }

  static Something decode(Object result) {
    result as List<Object?>;
    return Something(
      number: result[0]! as int,
    );
  }
}
```

Swift output:

```swift
struct Something {
  var number: Int64


  // swift-format-ignore: AlwaysUseLowerCamelCase
  static func fromList(_ pigeonVar_list: [Any?]) -> Something? {
    let number = pigeonVar_list[0] as! Int64

    return Something(
      number: number
    )
  }
  func toList() -> [Any?] {
    return [
      number
    ]
  }
}
```

Kotlin output:

```kotlin
data class Something (
  val number: Long
)
 {
  companion object {
    fun fromList(pigeonVar_list: List<Any?>): Something {
      val number = pigeonVar_list[0] as Long
      return Something(number)
    }
  }
  fun toList(): List<Any?> {
    return listOf(
      number,
    )
  }
}
```

### Code sample

<details open><summary>Code sample</summary>

```dart
@ConfigurePigeon(
  PigeonOptions(
    dartOut: 'lib/src/api.g.dart',
    kotlinOut:
        'android/src/main/kotlin/com/example/api/api/api.g.kt',
    swiftOut: 'ios/Classes/api.g.swift',
    kotlinOptions: KotlinOptions(package: 'com.example.api.api'),
  ),
)
class Something {
  final int number;

  Something({this.number = 5});
}
```

</details>

### Screenshots or Video

_No response_

### Logs

_No response_

### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
Doctor summary (to see all details, run flutter doctor -v):
[!] Flutter (Channel master, 3.26.0-1.0.pre.168, on macOS 14.5 23F79 darwin-arm64, locale en-RU)
    ! Warning: `dart` on your path resolves to /opt/homebrew/Cellar/dart/3.5.2/libexec/bin/dart, which is not inside your current Flutter SDK checkout at /Users/feduke-nukem/Desktop/git-projects/flutter/flutter. Consider adding
      /Users/feduke-nukem/Desktop/git-projects/flutter/flutter/bin to the front of your path.
    ! Upstream repository https://github.com/feduke-nukem/flutter is not a standard remote.
      Set environment variable "FLUTTER_GIT_URL" to https://github.com/feduke-nukem/flutter to dismiss this error.
[!] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    ! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses
[✓] Xcode - develop for iOS and macOS (Xcode 15.4)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2023.3)
[✓] VS Code (version 1.96.2)
[✓] Connected device (5 available)
[✓] Network resources

! Doctor found issues in 2 categories.
```

</details>