Improve/fix picking

[RandomShaper]

• Acknowledge mouse button events as position tellers (to make picking more solid; for instance, the touch mouse is raised with a mouse unpressed event that may have a more current position)
• Forget mouse position for physics if touch mouse raised (because the position known as last is no longer meaningful)
• Remove needless check for mouse over/exit (now there's code to inject an spurious move to ensure repicking if camera/objects have moved) <- @reduz, please confirm my assumption here is valid
• Restrict 2D mouse over/exit to mouse events (including emulated from touch; true touches shouldn't trigger the signals; they are just sent as events)
• Assign a device id of -1 to emulated mouse events

Fixes #26460.

[RandomShaper]

@akien-mga, I think a new beta would be needed after this one, before entering RC.

[akien-mga]

We don't really have time for another beta though... That's a big change at this stage right before RC. I'll see with @reduz if we take the risk or if it has to wait for 3.1.1.

[RandomShaper]

I can make a test project that ensures everything affected works, to be sure.
There's a small behavior change that would be nice to have in the final release, since it makes 2D and 3D picking work closer to how each other does.
My bad I didn't noticed it earlier. Not much time lately to contribute.