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/globals.h

@@ -1042,6 +1042,14 @@ typedef enum {
 #define MIN_CD_SCOPE  kCdScopeWindow
 #define MAX_CD_SCOPE  kCdScopeGlobal
 
+/// What caused the current directory to change.
+typedef enum {
+  kCdCauseOther = -1,
+  kCdCauseManual,  ///< Using `:cd`, `:tcd`, `:lcd` or `chdir()`.
+  kCdCauseWindow,  ///< Switching to another window.
+  kCdCauseAuto,    ///< On 'autochdir'.
+} CdCause;
+
 // Only filled for Win32.
 EXTERN char windowsVersion[20] INIT(= { 0 });