Explicit synchronization for PipeWire backend / syncobj for dmabuf
Prompted by !1584 (comment 2501970).
See also pipewire/pipewire#3947 (closed) and https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3876
This also implicitly needs an update from 0.X to 1.X as well, so there's probably a bit more work.