refactor: change Message kind into an enum instead of a String

[ckipp01]

While digging into Diagnostics there wasn't an easy way to tell all the
available kinds that there could be since they were just a string
value. So this small changes just makes the kind field in Message a
MessageKind which is an enum of all the types of message kinds that
exist.

[som-snytt]

Alternative to relying on toString everywhere

enum Thing:
  def message: String =
    this match
    case Other => "some other thing"
    case x => s"Thing $x"

  case One, Two, Other

@main def test() = println {
  Thing.values.to(List).map(_.message)
}

(Trying to recall if that is my first Scala 3 enum.)

[ckipp01]

Alternative to relying on toString everywhere

enum Thing:
  def message: String =
    this match
    case Other => "some other thing"
    case x => s"Thing $x"

  case One, Two, Other

@main def test() = println {
  Thing.values.to(List).map(_.message)
}

(Trying to recall if that is my first Scala 3 enum.)

The thing I'm afraid for with this though is that somewhere someone will just rely on the toString because they are used to it with enums. I sort of felt like this might be clearer. I think I'd rather do `Some Other Thing` first almost. Wdyt?

[som-snytt]

Oh, you mean they're used to "kind" being "just a string"? I would not sweat that. But I haven't looked closely at the interpolators for messaging. I hope they don't just toString. I saw Dale's "use show" PR but haven't looked twice yet. Maybe this is the moment when, as smarter would say, it becomes "principled". Others would say "reasonable".

[ckipp01]

Alright, I took your suggestion @som-snytt. Thanks!