`expr` failed to match multibyte character

[Luv-Ray]

regex engine should match the . to the multibyte characters.

> expr match 你好a ..a
3
> ./target/debug/coreutils expr match 你好a ..a
7

[Luv-Ray]

we are using onig (a wrapper around the Oniguruma regular expression library) to deal with regex, however, oniguruma will never support locale.

[RenjiSann]

Yes, this is why we can't completely pass the expr-multibyte.pl GNU test.

At some point if we want locale support for regexes, we will have to switch from oniguruma.

c.f. https://github.com/uutils/coreutils/pull/8292#discussion_r2192901229

[RenjiSann]

Fixed by #8606