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.
Like T92364 suggests, this patch changes the clickable area from this:
{F11320410}
To almost exactly this:
{F11320413}
The `Move Orientation:` labels on the left of the 3D View tool header can still be clicked through in this patch, otherwise it seems to match.
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Fixes T94016, T91538, T91579, T71899.