xwayland: clicks ignored in negative coords

1. Configure the Wayland compositor with a negative position for an output
2. Move an Xwayland window on that output
3. Clicks with a negative coordinate in the global compositor space are ignored

Is this a X11 protocol limitation? If so, a mitigation should be added to Xwayland (Wayland doesn't guarantee the outputs coords to be positive).

References: https://github.com/swaywm/wlroots/issues/958