core: resolve more specifiers in unit_name_printf()

core: resolve more specifiers in unit_name_printf()

unit_name_printf() is usually what we use when the resulting string shall
qualify as unit name, and it hence avoids resolving specifiers that almost
certainly won't result in valid unit names.

Add a couple of more specifiers that unit_full_printf() resolves also to the
list unit_name_printf() resolves, as they are likely to be useful in valid unit
names too. (Note that there might be cases where this doesn't hold, but we
should still permit this, as more often than not they are safe, and if people
want to use them that way, they should be able to.)