bug#52558: Option for easier typing of regexps

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: laszlomail@protonmail.com,  52558@debbugs.gnu.org
> Date: Wed, 29 Dec 2021 19:17:51 +0200
> 
> query-replace uses isearch functions to search the next occurrence to replace.
> The new variable replace-regexp-function is intended just to set
> the value of isearch-regexp-function that is used by isearch functions.
> And isearch-regexp-function already has 18 lines of its docstring
> that explains all details.  This is why it's important to have a link
> to isearch-regexp-function in the docstring of replace-regexp-function.

Thanks, I used this to clarify the doc string.