bug#28182: maybe implement CTRL++ to zoom text

[Eli Zaretskii]

> From: Richard Stallman <rms@gnu.org>
> Cc: stefan@marxist.se, homeros.misasa@gmail.com, juri@linkov.net,
>       28182@debbugs.gnu.org, jidanni@jidanni.org
> Date: Sun, 29 Sep 2019 11:33:58 -0400
> 
> I would find C-+ useful even if C-- does numeric arguments.
> C-- C-+ would shrink the font size.  Indeed, that is an easy
> combination to type.

It isn't so easy on my keyboard, where C-+ requires to press Shift.

Also, this is not what other applications out there provide for this
purpose, they provide C-mouse-wheel.  We already have "C-x C-+"
(actually, "C-x C-=", as pressing Shift is unnecessary) and its
counterpart "C-x C--", which are easy enough and don't get in the way
of other bindings.  How many different bindings do we need to have for
such an infrequent command?