Represent equivalent `enum`s the same as `bool`, make `bool` an `enum`

[CLICKME](https://github.com/glaebhoerl/rfcs/blob/make-bool-an-enum/active/0000-make-bool-an-enum.md)
I don't think we should force this - we currently reserve the right to change all our default data representations and that is nice flexibility to have. You can request this using the c-repr annotation, and of course you could put that on the bool enum, which fulfils your use case, I think.