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/shared/install-printf.c

@@ -98,7 +98,7 @@ static int specifier_last_component(char specifier, const void *data, const char
 }
 
 int install_name_printf(
-                LookupScope scope,
+                RuntimeScope scope,
                 const InstallInfo *info,
                 const char *format,
                 char **ret) {