bug#56691: outline-minor-mode displays navigation arrow buttons as emojis

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: hello@paulwrankin.com,  56691@debbugs.gnu.org
> Date: Thu, 28 Jul 2022 14:37:17 +0200
> 
> Lars Ingebrigtsen <larsi@gnus.org> writes:
> 
> > I sorta decided to rework how icon/button selection works at the same
> > time, so it'll take some more time to work out all the kinks in this
> > area.
> 
> I've now done this.  And note that customizing the buttons has now
> changed completely, see (emacs)Icons for details.

Thanks.

The test for Emoji display is not accurate enough.  Maybe we should
have a display-color-emoji-p predicate?  I added a FIXME there.