hashmap: Add helper to dump sorted keys

Currently, hashmap_dump_sorted sorts by key and then returns the values
in order sorted by key. This commit adds another helper that does the
same but returns the sorted keys instead

src/basic/hashmap.h

@@ -409,6 +409,14 @@ static inline int set_dump_sorted(Set *h, void ***ret, size_t *ret_n) {
         return _hashmap_dump_sorted(HASHMAP_BASE(h), ret, ret_n);
 }
 
+int _hashmap_dump_keys_sorted(HashmapBase *h, void ***ret, size_t *ret_n);
+static inline int hashmap_dump_keys_sorted(Hashmap *h, void ***ret, size_t *ret_n) {
+        return _hashmap_dump_keys_sorted(HASHMAP_BASE(h), ret, ret_n);
+}
+static inline int ordered_hashmap_dump_keys_sorted(OrderedHashmap *h, void ***ret, size_t *ret_n) {
+        return _hashmap_dump_keys_sorted(HASHMAP_BASE(h), ret, ret_n);
+}
+
 /*
  * Hashmaps are iterated in unpredictable order.
  * OrderedHashmaps are an exception to this. They are iterated in the order