bug#38187: 27.0.50; No mouse-wheel scaling on images

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Date: Tue, 12 Nov 2019 22:38:12 +0200
> 
> Tried to use a new recently added useful feature of using C-mouse-wheel to 
> zoom.
> 
> But it seems it has no effect on images, at least its effect is not visible:
> it doesn't scale images in image mode.

  <C-wheel-up> at that spot runs the command mouse-wheel-text-scale
  (found in global-map), which is an interactive compiled Lisp function
  in ‘mwheel.el’.

  It is bound to <C-wheel-down>, <C-wheel-up>.

  (mouse-wheel-text-scale EVENT)

  Increase or decrease the height of the default face according to the EVENT.

It is documented to increase/decrease the size of _text_ of the
default face.  It isn't documented to "zoom", which is a much more
general action/effect.