Highlight parts of images

[ischurov]

It should be possible to highlight a part of an image on hover over special kind of a reference. Something like this:

Let's consider \imref[fig12][point-x][point $x$].

Then on hover on text point $x$, the corresponding point should be highlighted on figure fig12.

Not clear what to do if fig12 is currently not visible. Probably, on mobile we should open it in a modal. Not sure about desktop.