src/basic: rename uid-alloc-range.[ch] to uid-classification.[ch]

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the existing name is outdated.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.

src/sysusers/sysusers.c

@@ -35,7 +35,7 @@
 #include "strv.h"
 #include "sync-util.h"
 #include "tmpfile-util-label.h"
-#include "uid-alloc-range.h"
+#include "uid-classification.h"
 #include "uid-range.h"
 #include "user-util.h"
 #include "utf8.h"