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

[emacsq]

> Then need to wait when someone will step forward to write these
> BRE/ERE/PCRE translation functions.

This is a bigger job and is there a current need for it?

People just want to make their life easier and change the way
how the syntax of some of the symbols often used by them works
in interactive input (e.g. grouping).

If we wait for those complete translation functions then we
might have to wait for a long time, unless there are people
who want complete translations right now, but there were no
such volunteers in this thread for that task.

Adding an option for a custom translation function solves the
problem right know, everyone can change the symbols they are
most annoyed by and this function can be the base mechanism
for complete translations later if someone ever wants to do
those.