bug#65854: Multi-file replacement diff

[Juri Linkov]

>> As discussed on emacs-devel, here is the patch that implements
>> a standalone command that reads a list of files and replacement strings,
>> then shows a diff to review before applying replacements.
>> Also provided the Dired integration to show the replacement diff
>> on marked files.  Later the same function could be used
>> to show replacement diffs from the xref buffer and maybe
>> from other packages as well.
>
> Here's a counter-proposal: we were talking about a "refactoring" packages
> on emacs-devel, maybe a week ago. And I suggested a function that would
> take a list of changes (as some data) and present them using some
> customizable logic: the current Eglot's solution uses a diff, and I'll add
> an implementation that shows a tree-like buffer with checkmarks, probably.
>
> I'll be starting on this any day now ;-(
>
> So... provided this won't take too long, I would suggest your code here
> just focuses on creating a list of changes (those shouldn't require buffers
> to visit files), and then you'd be able to pass them on to
> 'refact-show-changes' (name under construction), which would then use the
> interface that the user prefers.
>
> This was we'll also consolidate the diff-generating code for features of
> this sort.

I'm not sure this complication is necessary.  The proposed patch
does its job already.  So more generalizations could be added later.