bug#31796: 27.1; dired-do-find-regexp-and-replace fails to find multiline regexps

[Juri Linkov]

>> dired-do-find-regexp uses 'ignores' to filter out ignored files.
>> You could add another filter to filter out files without matches
>> using 'grep -PzL'.
>
> Right. This is sorta a backup plan. Although, when the number of files to
> search can be counted on one hand, there's nothing too bad in doing the
> search in Emacs.

Another backup plan is to use ripgrep.  Its multiline handling with -U
also allows to search words ignoring any whitespace, even newlines.
This is like isearch-lax-whitespace using search-whitespace-regexp
when it contains a newline, e.g. "[ \t\r\n]+".