patch 8.2.3320: some local functions are not static

Problem:    Some local functions are not static.
Solution:   Add "static".  Move snprintf() related code to strings.c.
            (Yegappan Lakshmanan, closes #8734)

src/dict.c

@@ -805,7 +805,7 @@ dict2string(typval_T *tv, int copyID, int restore_copyID)
  * Advance over a literal key, including "-".  If the first character is not a
  * literal key character then "key" is returned.
  */
-    char_u *
+    static char_u *
 skip_literal_key(char_u *key)
 {
     char_u *p;