basic: add RuntimeScope enum

In various tools and services we have a per-system and per-user concept.
So far we sometimes used a boolean indicating whether we are in system
mode, or a reversed boolean indicating whether we are in user mode, or
the LookupScope enum used by the lookup path logic.

Let's address that, in introduce a common enum for this, we can use all
across the board.

This is mostly just search/replace, no actual code changes.

src/sysv-generator/sysv-generator.c

@@ -745,7 +745,7 @@ static int enumerate_sysv(const LookupPaths *lp, Hashmap *all_services) {
                         if (hashmap_contains(all_services, name))
                                 continue;
 
-                        r = unit_file_exists(LOOKUP_SCOPE_SYSTEM, lp, name);
+                        r = unit_file_exists(RUNTIME_SCOPE_SYSTEM, lp, name);
                         if (r < 0 && !IN_SET(r, -ELOOP, -ERFKILL, -EADDRNOTAVAIL)) {
                                 log_debug_errno(r, "Failed to detect whether %s exists, skipping: %m", name);
                                 continue;
@@ -889,7 +889,7 @@ static int run(const char *dest, const char *dest_early, const char *dest_late)
 
         assert_se(arg_dest = dest_late);
 
-        r = lookup_paths_init_or_warn(&lp, LOOKUP_SCOPE_SYSTEM, LOOKUP_PATHS_EXCLUDE_GENERATED, NULL);
+        r = lookup_paths_init_or_warn(&lp, RUNTIME_SCOPE_SYSTEM, LOOKUP_PATHS_EXCLUDE_GENERATED, NULL);
         if (r < 0)
                 return r;