bug#54296: Add buffer-matching functionality

[Eli Zaretskii]

> From: Philip Kaludercic <philipk@posteo.net>
> Cc: larsi@gnus.org,  54296@debbugs.gnu.org
> Date: Thu, 14 Apr 2022 08:25:58 +0000
> 
> >> > I suggested to "clarify" that by not providing the 'major-mode'
> >> > predicate at all.  I still don't think I understand why it is so
> >> > important that we should provide a special case for it.
> >> 
> >> It is not inherently important, it is just that if the predicate would
> >> also be used in project.el, then compatibility would have to be broken,
> >> as the distinction between `major-mode' and `derived-mode' exists there.
> >
> > Then project.el could use the predicate route, right?  It's quite a
> > special case, AFAIU, so having a special solution is OK.
> 
> I have updated the commits as you recommended, and add a commit
> deprecating the use of `derived-mode' in project.el.

Thanks, LGTM.