Packaging Stdune.Ansi_color as a separate package

[mbarbin]

I started using this module a while ago and I find it really useful in conjunction to using the package pp for building styled error messages in a functional way. I would find it easier to re-use in various contexts and published opam packages if it wasn't part of stdune (due to the warning about stdune being unstable). It seems it only depends on foundational packages (pp, ordering, .. ?).

I'm thinking of names such as pp_tty, or pp_ansi, add a type t = Style.t list Pp.t in it, and good to go!

What do you think? The lift/refactor seems easier that loc (#10948) at this time, but I haven't actually tried.

You see, the interface of Pp is great, but because the type of tags is left for the user to instantiate, there isn't any good default for using pp for clis, and user facing error messages. My impression is that Pp_tty.t would have the potential to become such standard.

[rgrinberg]

Sure, sounds fine to me. You would have to lead the effort though