lua: coordinates should always be in OSD resolution

This has to be done specially for the input section mouse area.
input: trigger mouse_leave key bindings if mouse leaves mouse area
osc: replace deadzone handling with mouse input area

set_mouse_area() sets the region where mouse events should be received.
Outside this area, mouse events are handled normally (and for example
use the user's normal input.conf bindings). Also, leaving the mouse area
triggers the mouse_leave binding. (Mouse enter is already covered by
mouse_move.)

So, set the mouse area to the OSC (non-deadzone) area. Make sure the OSC
is visible when entering the area (mouse_move), and hiding the OSC when
the mouse goes outside (mouse_leave). As a bonus, it will be possible to
hide the OSC if the mouse cursor leaves the window entirely (but that
requires support from the VO).
x11_common: trigger mouse_leave key bindings when mouse leaves window
input: fix NULL deref in input-test mode
don't hide mouse cursor if mouse is inside osc region