bug#44611: Prefix arg for xref-goto-xref

[Juri Linkov]

>> > I'm okay with this distinction, provided we decide that we will try to
>> > keep only these two variants, as much as possible.
>>
>> Let me get this straight:
>>
>> You oppose changing the TAB binding, which is currently documented to be
>> present in the UI for both cases (and *is* present).
>>
>> But you're fine with creating a +1 subtly different behavior between the
>> cases, by changing the TAB binding in only one of them?
>
> Not exactly.
>
> I still prefer that we don't change the TAB binding at all.  But since
> Juri applies pressure (and evidently doesn't consider this difference
> between the behaviors in these two cases to be an issue), I yield to
> that pressure by the above compromise.

I'm not pressuring anyone, mind you.  This is part of efforts to develop
project-find-regexp as a replacement of rgrep.  The previous task was
to remove duplicate output lines that is successfully completed now.
The next tasks are support for multi-line search strings, word search, etc.
Bringing keybindings of project-find-regexp closer to grep mode is one
of such tasks that will help the users to adapt grep usage patterns to
project-find-regexp and other grep-like xref commands.