systemctl: Add --with-dependencies flag

systemctl: Add --with-dependencies flag

Will print a unit and all of its dependencies. Works with cat, status,
list-units, and list-unit-files. This flag can also be used in conjunction
with --reverse, --before, and --after.

We also vastly simplify the list_dependencies_get_dependencies logic.
Instead of using 5 strvs and merging them into one, use one strv and
have the bus append all the map values to it.

Fixes #9273