Trailing commas for enhanced enums are not preserved

```dart
enum MyEnum {
  pending('pending'),
  awesome('awesome'),
  completed('completed'),
  ;

  const MyEnum(this.value);

  final String value;
}
```

This gets formatted into, even when trailing commas are preserved:
```dart

enum MyEnum {
  pending('pending'),
  awesome('awesome'),
  completed('completed');

  const MyEnum(this.value);

  final String value;
}
```