vim-patch:8.0.1459: cannot handle change of directory

Problem:    Cannot handle change of directory.
Solution:   Add the DirChanged autocommand event. (Andy Massimino,
            closes vim/vim#888)  Avoid changing directory for 'autochdir' too often.
b7407d3fc9

Only add "auto" pattern. "window" and "global" are already implemented.
Skip `Test_dirchanged_auto` using `CheckFunction test_autochdir`.
Part of PR #15952. More information can be found there.

N/A patches for version.c:

vim-patch:8.0.1460: missing file in patch

Problem:    Missing file in patch.
Solution:   Add changes to missing file.
b5cb65ba2b

vim-patch:8.0.1461: missing another file in patch

Problem:    Missing another file in patch.
Solution:   Add changes to missing file.
15833239a4

src/nvim/ex_docmd.c

@@ -7749,7 +7749,7 @@ void post_chdir(CdScope scope, bool trigger_dirchanged)
   shorten_fnames(true);
 
   if (trigger_dirchanged) {
-    do_autocmd_dirchanged(cwd, scope, false);
+    do_autocmd_dirchanged(cwd, scope, kCdCauseManual);
   }
 }