Re-evaluate icecave dependency

[W0rma]

#518 added the dependency to icecave/parity.

In composer/composer#12039 (comment) it was recommended to check whether this dependency is really necessary:

At some point we maybe should (re-) evaluate them. Especially the icecave/* seems the odd one out as it is advertised as a A customizable deep comparison library. Which seems unneeded at a quick glance.

I just created this issue to not forget about this evaluation.

[DannyvdSluijs]

Thanks for issue report. Is this something you've already did some investigation into or have some knowledge about?
Or is it purely a reminder at this point?

[W0rma]

It's purely a reminder.
I haven't done any research yet.

[erayd]

@W0rma The dependency on icecave/parity was added in order to fix an issue with deep comparison of objects in the enum & const constraint validation. PHP did not at the time have a native mechanism to do it properly (is that still the case?)

An alternative to the dependency would be to implement proper deep comparison in this library.

[petski]

justinrainbow/json-schema 6.0.0 requires icecave/parity (1.0.0) 
icecave/parity 1.0.0 requires icecave/repr (~1) 

Both icecave/* dependencies were released 10+ years ago. I found out that icecave/repr even has a file on board (see ./vendor/icecave/repr/src/Generator.php:229) that isn't parsable since PHP 8.0. A fix is already present in icecave/repr@9ccbaec (5 years ago) though...

PHPUnit has a (very) good way of comparing "things", and PHPUnit's author has released the compare component under https://github.com/sebastianbergmann/comparator. It may be a good candidate to swap out icecave/* for sebastianbergmann/comparator (?)