mount: make sure we unmount tmpfs mounts before we deactivate swaps (#7076)

In the past we introduced this property just for tmp.mount. However on
todays systems usually there are many more tmpfs mounts. Most notably
mounts backing XDG_RUNTIME_DIR for each user.

Let's generalize what we already have for tmp.mount and implement the
ordering After=swap.target for all tmpfs based mounts.