When zooming have mouse cursor stay at the same position to the image.
When I zoom, then the position of the image that the mouse cursor pointed to while zooming gets put exactly in the middle of the screen. A better approach would be to have it like Gimp, where the mouse cursor essentially stays at the same pixel.
I could also try to implement it myself if someone could help me understand these variables, from line 348 to 370: https://gitlab.gnome.org/GNOME/gthumb/-/blob/master/gthumb/gth-image-viewer.c#L346