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the existing name is outdated.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/basic/meson.build

@@ -96,7 +96,7 @@ basic_sources = files(
         'terminal-util.c',
         'time-util.c',
         'tmpfile-util.c',
-        'uid-alloc-range.c',
+        'uid-classification.c',
         'uid-range.c',
         'unit-def.c',
         'unit-file.c',