Fix possible crash when Control overrides mouse input on Area2D

[KurtBliss]

Made Viewport::_cleanup_mouseover_colliders queue up mouse_exit and mouse_shape_exit signals to emit and at the end of the function's execution to avoid potential crashes.

Fixes #79371

[Sauermann]

The reason for the crash was that during a for(const KeyValue<ObjectID, uint64_t> &E : physics_2d_mouseover)-loop the variable physics_2d_mouseover was changed.

So this fix makes sense independently of my initial thoughts regarding mouse-over handling.

Have tested the PR with the MRP of the linked issue and can no longer replicate the crash.

[KurtBliss]

I was thinking at first this method would be good incase of another function or variable could retrigger Viewport::_cleanup_mouseover_colliders immediately like changing the control.mouse_default_cursor_shape in the MRP. But after checking if using the get_viewport().warp_mouse(position : Vector2) could cause a immediate retrigger, it didn't, idk may of been better with Sauermann initial thought on it. Not really sure.

[akien-mga]

Thanks!