Blender Git Loki

Fix T83935: Superimposed icon's hotspot is misaligned

Now the icon's rect are drawn wider than it should be, and with
overlapping, probably in order to compensate for the icon's offsets
inside the rect. The solution is to draw icon's rect of the correct
size and center the icon itself.

And make the hotspot exactly match the icon's rect. The last/right
button's hotspot also covers the extra padding on the right.

Differential Revision: https://developer.blender.org/D9936

Reviewed by: Julian Eisel