expr: revert replacement of onig with fancy-regex

[wtcpython]

I'm really sorry for the trouble this caused. This reverts #14329 to restore the previous behavior.

[Copilot]

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[oech3]

Cannot you contribute to fancy-regex instead? The PR itself does not regress anything yet.
We need to remove oniguruma at some time.

[oech3]

I think we don't need to revert comments about openssl because it is unrelated.

[github-actions]

Binary size comparison:

Individual binary size comparison VS main (threshold: >=5% AND >=4 KB).

Total size of compared binaries: 152.18 MB (-912 KB, -0.58%)

Significant per-binary changes:
  expr     3.65 MB ->    2.76 MB  (-908 KB, -24.30%)

[xtqqczze]

@sylvestre Maybe we should consider this for coreutils 0.12. But I think it’s preferable not to revert for now, so we can find more bugs and fix them upstream.

[oech3]

Unfortunately, many people does not report bugs from non-stable commit...
(Also note that latest-commit is distributing outdated binaries)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/tail/tail-n0f is now being skipped but was previously passing.

[keith-hall]

#14527

[oech3]

@keith-hall Is this not part of fancy-regex yet (does uutils still need it)?

[keith-hall]

fancy-regex doesn't have a parse flag for BRE syntax yet, no, so uutils still needs it

[oech3]

Close this PR as resolved.