patch 8.2.4335: no autocommand event triggered before changing directory

Problem:    No autocommand event triggered before changing directory. (Ronnie
            Magatti)
Solution:   Add DirChangedPre. (closes #9721)
diff --git a/src/proto/ex_docmd.pro b/src/proto/ex_docmd.pro
index 0fed2f0..3be7471 100644
--- a/src/proto/ex_docmd.pro
+++ b/src/proto/ex_docmd.pro
@@ -48,6 +48,7 @@
 void do_exedit(exarg_T *eap, win_T *old_curwin);
 void free_cd_dir(void);
 void post_chdir(cdscope_T scope);
+void trigger_DirChangedPre(char_u *acmd_fname, char_u *new_dir);
 int changedir_func(char_u *new_dir, int forceit, cdscope_T scope);
 void ex_cd(exarg_T *eap);
 void do_sleep(long msec, int hide_cursor);