This introduces -DWLR_USE_UNSTABLE and adds information regarding the
stability status to all headers. I started with a conservative set of
headers to mark as stable:
- types/wlr_matrix.h
- util/edges.h
- util/log.h
- util/region.h
- xcursor.h
There was no way to tell wlr_idle to stop processing input events
and rearm timers all the time, such an API is required to have
some form of idle inhibitor.
This moves the `struct wl_signal activity_notify` in `struct wlr_idle`
into a local `struct {} events` to keep consistency with other modules
in the library.