userdbctl: add some basic client-side filtering

This adds some basic client-side user/group filtering to "userdbctl":

1. by uid/gid min/max
2. by user "disposition" (i.e. show only regular users with "userdbctl
   user -R")
3. by fuzzy name (i.e. search by substring/levenshtein of user name,
   real name, and other identifiers of the user/group record).

In the long run we also want to support this server side, but let's
start out with doing this client-side, since many backends won't support
server-side filtering anytime soon anyway, so we need it in either case.

src/shared/user-record.h

@@ -462,6 +462,24 @@ int user_group_record_mangle(sd_json_variant *v, UserRecordLoadFlags load_flags,
 #define BLOB_DIR_MAX_SIZE (UINT64_C(64) * U64_MB)
 int suitable_blob_filename(const char *name);
 
+typedef struct UserDBMatch {
+        char **fuzzy_names;
+        uint64_t disposition_mask;
+        union {
+                uid_t uid_min;
+                gid_t gid_min;
+        };
+        union {
+                uid_t uid_max;
+                gid_t gid_max;
+        };
+} UserDBMatch;
+
+#define USER_DISPOSITION_MASK_MAX ((UINT64_C(1) << _USER_DISPOSITION_MAX) - UINT64_C(1))
+
+bool user_name_fuzzy_match(const char *names[], size_t n_names, char **matches);
+int user_record_match(UserRecord *u, const UserDBMatch *match);
+
 const char* user_storage_to_string(UserStorage t) _const_;
 UserStorage user_storage_from_string(const char *s) _pure_;