[Feature request] Generate static property to get key strings.

[normidar]

Is your feature request related to a problem? Please describe.
Similer with #437

Describe the solution you'd like

I use key to access my Json after toJson() so I create codes like:

@freezed
class TaskDataset with _$TaskDataset {
  // ↓ here
  static const keyTask = 'task';
  static const keyIsDone = 'isDone';
  static const keyCreatedAt = 'createdAt';
  static const keyStared = 'stared';
  // ↑ here

  const factory TaskDataset({
    required String task,
    required bool isDone,
    required DateTime? createdAt,
    bool? stared,
  }) = _TaskDataset;

  factory TaskDataset.fromJson(Map<String, dynamic> json) =>
      _$TaskDatasetFromJson(json);
}

I need a way to generate them.

Describe alternatives you've considered
As above

Additional context
I search and find #437 , but I thing this issue is different.

[rrousselGit]

That's even worse than #437 :P

JSON logic isn't part of Freezed but json_serializable. Freezed won't do such a thing.

But to begin with, what you're asking is already part of json_serializable, under the name createFieldMap: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonSerializable/createFieldMap.html