backend/drm: add support for suggested output position prop
Depends on and includes commits from https://github.com/swaywm/wlroots/pull/2628 (could also be independently rebased onto master)
Relates to https://github.com/swaywm/wlroots/issues/2188
Virtualised outputs use the "suggested X" and "suggested Y" DRM props to indicate their relative position on the host WM.
This change adds members suggested_x
and suggested_y
to struct wlr_output
which contain the value of these props. Also, a suggested_position
signal is added so that compositors can be notified if there is a changed in the suggested position.