refactor: run IWYU on entire repo

Reference: https://github.com/neovim/neovim/issues/6371.

src/nvim/undo.c

@@ -77,7 +77,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/types.h>
 #include <time.h>
 #include <uv.h>
 
@@ -106,6 +105,7 @@
 #include "nvim/highlight.h"
 #include "nvim/macros_defs.h"
 #include "nvim/mark.h"
+#include "nvim/mbyte.h"
 #include "nvim/memline.h"
 #include "nvim/memory.h"
 #include "nvim/message.h"