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

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: Dmitry Gutov <dgutov@yandex.ru>,  joaotavora@gmail.com,
>   44611@debbugs.gnu.org
> Date: Thu, 24 Dec 2020 22:19:16 +0200
> 
> With further development of the search commands based on xref, more
> users perceive it as a grep replacement, that however is not based
> on grep mode, so this is a good reason to make xref keybindings more
> compatible with grep mode.

You didn't answer my question why not use the format we use in *grep*
buffers or *occur* buffers.

> > Given the single precedent I found, I'm fine with declaring the
> > current binding of TAB obsolete and providing a replacement for it
> > ('b'? 'q'?), so that we could replace it in some future version after
> > 28, if that is okay with you and Juri.
> 
> Thanks, this is surely okay.  So here is the patch that does this.
> It binds 'xref-quit-and-goto-xref' to 'C-j' like in icomplete mode:

That's not what I meant: I meant to leave the TAB binding for now at
what it is now, while declaring it obsolete in NEWS, and provide an
alternative for it that will remain when we rebind TAB to another
command.  But the rebinding of TAB will have to wait until after Emacs
28.  That's the meaning of "obsolete": we don't remove it right away,
but first warn users to get prepared for a removal in the future.

And why C-j?  That's LFD, a key more suitable for acting on something
at point, not quitting the buffer.  Why not 'q' (for "quit") or 'b'
(for "bury")?