Quote and escape in QCheck.Print.{char,string}, aligning it with QCheck2.Print

[jmid]

As mentioned in #296

• the QCheck.Observable.{char,string} function printers yield unhelpful output, despite using QCheck.Print.{char,string}
• quickfixing it like Quote and escape Observable strings and chars #296, adds another ad-hoc copy, rather than fixing the root cause, namely QCheck.Observable.{char,string}
• QCheck2.Print.{char,string} already quotes and escapes, creating a QCheck.Print / QCheck2.Print mismatch for chars and strings

This PR thus suggests the breaking change of fixing QCheck.Print.{char,string}.
This further opens up for cleaning up some of the ad-hoc printers in the arbitrary combinators (commit d1c1fee)

I'm hoping for fellow QCheck users and developers to chip in to the discussion and share which PR and QCheck2.Print.{char,string} they prefer... 🙏 🙂

[jmid]

To assess if this change would break anything I've rolled an opam-repo PR ocaml/opam-repository#27038
The conclusion is clear: there were (the usual) failures but none caused by QCheck.Print.{char,string} printers changing to properly quote and escape.

Based on this experiment I therefore favor this one over #296. OK with you @c-cube?

[jmid]

Rebased on main after merging #298

[jmid]

Looking again at our workaround in multicoretests I was reminded that bytes has the same problem - in both QCheck.Print and in QCheck2.Print.

The latest commits thus fix Print.bytes too.

The expect test updates in d8f3b5f and f773f75 document why this helps the end-user output.

[jmid]

Rebased on main after merging #302

[jmid]

OK. Since no objections have surfaces I'll go ahead and merge this one.