fs-util: rename path_is_safe() → path_is_normalized()

Already, path_is_safe() refused paths container the "." dir. Doing that
isn't strictly necessary to be "safe" by most definitions of the word.
But it is necessary in order to consider a path "normalized". Hence,
"path_is_safe()" is slightly misleading a name, but
"path_is_normalize()" is more descriptive, hence let's rename things
accordingly.

No functional changes.

src/basic/unit-name.c

@@ -382,7 +382,7 @@ int unit_name_path_escape(const char *f, char **ret) {
         if (STR_IN_SET(p, "/", ""))
                 s = strdup("-");
         else {
-                if (!path_is_safe(p))
+                if (!path_is_normalized(p))
                         return -EINVAL;
 
                 /* Truncate trailing slashes */
@@ -432,7 +432,7 @@ int unit_name_path_unescape(const char *f, char **ret) {
                 if (!s)
                         return -ENOMEM;
 
-                if (!path_is_safe(s)) {
+                if (!path_is_normalized(s)) {
                         free(s);
                         return -EINVAL;
                 }