Generate field names as strings similar to C# nameof operator

I would like to ask you to consider adding functionality that would generate field names to strings that would be accessible as static members of a class or an enum.

For example I am using [reactive_forms](https://pub.dev/packages/reactive_forms) package. When defining formgroup object, I have to use string literals for map keys which creates room for errors.
```
FormGroup({
'name': FormControl(),
'email': FormControl(),
});
```

I would much rather have something like this (static class members):
```
FormGroup({
User.fields.name: FormControl(),
User.fields.email: FormControl(),
});
```
or enum style:
```
FormGroup({
UserFields.name.name: FormControl(),
UserFields.email.name: FormControl(),
});
```

This would be useful for many more use cases, but this is the main for me.

Thank you for developing this wonderful library!