A bit confusingly CONTAINER_UID_BASE_MAX is just the maximum *base* UID
for a container. Thus, with the usual 64K UID assignments, the last
actual container UID is CONTAINER_UID_BASE_MAX+0xFFFF.
To make this less confusing define CONTAINER_UID_MIN/MAX that add the
missing extra space.
Also adjust two uses where this was mishandled so far, due to this
confusion.
With this change the UID ranges we default to should properly match what
is documented on https://systemd.io/UIDS-GIDS/.
We had both uid-range.h and uid-alloc-range.h. The latter now contains helpers
like {uid,gid}_is_{system,dynamic,container}(), uid_for_system_journal(), so
the existing name is outdated. I think the uid-range.[ch] should stay separate
because it has a bunch of helpers for parsing and printing of uid ranges. So
let's rename as in $subject to better reflect the contents of the file and make
the two sets of files harder to confuse.
