vim-patch:8.2.4366: not enough tests for command line completion

Problem:    Not enough tests for command line completion.
Solution:   Add a few more tests. (Yegappan Lakshmanan, closes vim/vim#9760)

4d03d87000

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

src/nvim/cmdexpand.c

@@ -103,6 +103,7 @@ static int sort_func_compare(const void *s1, const void *s2)
   return strcmp(p1, p2);
 }
 
+/// Escape special characters in the cmdline completion matches.
 static void ExpandEscape(expand_T *xp, char_u *str, int numfiles, char **files, int options)
 {
   int i;