bug#53181: Live preview of regexp replace

[ndame]

> This is exactly what Augusto is currently doing in bug#53126.

I checked it and it's not the same. It says:

" the highlighting and count of matches as one types a regexp or string to
replace in `query-replace{-regexp}'."

So it may do the first part, the highlighting of the regexp pattern while 
typing,
but it does not seem to do the second part, that is showing the replacement 
effects
in the buffer immediately as the user types the replacement text or pattern.

The second part is just as important, because that shows if the actual 
replacement
is correct or it needs some tweaking before starting replacing.