date: use jiff-icu for locale calendar conversions

[ChrisDryden]

This is the approach I would use by just directly using jiff-icu to perform the conversions and not having to create new icu dates to get the ICU localizations. I think this approach is much more extensible to be able to cover all of the different formatters and modifiers.

I also added a few more regression tests for the localizations that we have so far so that we don't regress with the localizations we've made already as we add more features

[sylvestre]

i am now ashamed of my previous iteration :)
well done!

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/retry. tests/tail/retry is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)