bug#54017: add regexp translation option to read-regexp

[emacsq]

> I originally interpreted the OP's request as asking for a feature
> where the user could use one of the regexp styles used by other
> programs, such as BRE or ERE or maybe PCRE.

If it provides me a more friendly regexp syntax where I don't have to
qoute parens, alternations then I'm OK with it, though I guess
providing a full translation for certain styles is much more work,
so giving an option for translation and letting the user write his
own function according to his taste may be the simpler solution which
can even support different custom regexp styles later.