Place launched applications into a systemd scope
This improves separation from the gnome-panel service scope. This is important for systemd-oomd users, which kills all processes within a scope when the configured limits are exceeded.
The logic comes from GNOME Shell: https://gitlab.gnome.org/GNOME/gnome-shell/-/blob/751fedb95cbb56ff23bb75ddb6e9a2210a8265c2/src/shell-global.c?page=2#L1414-1428
Related merge request for GNOME Shell: gnome-shell!863 (merged)