Does two main changes: * Handle regions in the order as visible on screen. Practically this just means handling overlapping regions before non-overlapping ones. * Don't handle any other regions after having found one containing the mouse pointer. Fixes: T94016, T91538, T91579, T71899 (and a whole bunch of duplicates) Addresses: T92364 Differential Revision: https://developer.blender.org/D13539 Reviewed by: Campbell Barton