Creates a `GtkDragIcon` that shows paintable, and associates it with the drag operation.
The hotspot position on the paintable is aligned with the hotspot of the cursor.
| drag |
a `GdkDrag` |
| paintable |
a `GdkPaintable` to display |
| hot_x |
X coordinate of the hotspot |
| hot_y |
Y coordinate of the hotspot |