bug#67794: 30.0.50; mouse-face is not respected on SVG images

[Eli Zaretskii]

> From: Manuel Giraud <manuel@ledu-giraud.fr>
> Cc: Eli Zaretskii <eliz@gnu.org>,  gerd.moellmann@gmail.com,
>   67794@debbugs.gnu.org
> Date: Tue, 19 Dec 2023 13:45:03 +0100
> 
> > I believe that we need to do some final set-up for the image under
> > X/GTK/whatever and it looks as though this is all that's needed:
> >
> >      id = lookup_image (f, s->img->spec, hlinfo->mouse_face_face_id);
> >      s->img = IMAGE_FROM_ID (f, id);
> >      prepare_image_for_display (f, s->img); <------
> >
> > Under X we need to send the image to the X server, and under Cairo it
> > does some other stuff. That's what prepare_image_for_display does. It
> > does nothing under NS, so the image worked fine under GNUstep.
> 
> Thank you Alan!  That does the trick.  So here is an updated version of
> the patch that works with XRender (i'll test with cairo).

With this change, if you move the mouse pointer on and off the image
several times, what happens to the Emacs memory footprint?
Specifically, how many times is memory allocated for the SVG image,
and if it's allocated each time, does it ever get deallocated?