bug#37073: 26.2.90; query-replace-regexp undo feature missing quote the regexps

[Juri Linkov]

> That causes the undo feature to fail if the replacement contains special 
> characters.

Thanks.  Are there other looking-at/looking-back occurrences
in perform-replace that are looking at non-regexp strings?

> commit 9f9c56cfa99b1e6fe296ec591ab335521e185e55
> Author: Tino Calancha <tino.calancha@gmail.com>
> Date:   Sun Aug 18 15:57:59 2019 +0200
>
>     Fix query-replace-regexp undo feature
>
>     * lisp/replace.el (perform-replace): Quote regexp (Bug#37073).
>     * test/lisp/replace-tests.el (query-replace-undo-bug37073): Add test

This looks good, but please ask Eli about pushing it to emacs-26 branch.
Recently we fixed another problem exactly in the same place,
but pushed the fix to the master.