Dragging tabs makes mouse jump to left side of tab

[Gijs (Gijs de Zwart)]

Continuing the discussion from Rhino 8 UI panel-related woes:

@anon

Tab drag preview position is wrong unless you click on the left side of it. If you grab the right side of a tab and try to drag it, the drag preview displays as if you clicked the left side. This is surprising behavior and misleads the user.