Don't try to find the card, and then the render node from it, just ask
udev to list the render nodes directly. This avoids running into
permission errors when the user cannot open /dev/dri/card* even without
mode setting capabilities.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3805>
Instead of testing headless start using the dummy backend, do so with
the real native backend, and use the drm-mock library instead to emulate
monitors being disconnected at startup.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2821>
This new filter allows test cases to manipulate what the kernel reports,
e.g. mark connected connectors as disconnected to emulate monitors
connecting and disconnecting.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2821>