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

[積丹尼 Dan Jacobson]

This morning I finally switched from
$ xrandr --output DP-1 --mode 1920x1080 #to
$ xrandr --output DP-1 --mode 1680x1050
and now can read things comfortably again.

About that text zooming key binding stuff,
maybe make them part (info "(emacs) CUA Bindings").
That seems where the CTRL++ and CTRL+- overrides belong.
If the user is rebinding C-c and C-x etc. then he probably also wants
the zoom overrides for CTRL++ and CTRL+- he is familiar with.

(I'm not exactly sure how close all this is to
https://en.wikipedia.org/wiki/IBM_Common_User_Access etc.)