fix(api): ignore 'autochdir' when renaming other buf (#28376)

Problem:  Renaming non-current buffer changes working directory when
          'autochdir' is set.
Solution: Temporarily disable 'autochdir'.  Add more tests for the
          win_set_buf change.

src/nvim/api/buffer.c

@@ -39,6 +39,7 @@
 #include "nvim/memory_defs.h"
 #include "nvim/move.h"
 #include "nvim/ops.h"
+#include "nvim/option_vars.h"
 #include "nvim/pos_defs.h"
 #include "nvim/state_defs.h"
 #include "nvim/types_defs.h"
@@ -984,12 +985,23 @@ void nvim_buf_set_name(Buffer buffer, String name, Error *err)
 
   try_start();
 
+  const bool is_curbuf = buf == curbuf;
+  const int save_acd = p_acd;
+  if (!is_curbuf) {
+    // Temporarily disable 'autochdir' when setting file name for another buffer.
+    p_acd = false;
+  }
+
   // Using aucmd_*: autocommands will be executed by rename_buffer
   aco_save_T aco;
   aucmd_prepbuf(&aco, buf);
   int ren_ret = rename_buffer(name.data);
   aucmd_restbuf(&aco);
 
+  if (!is_curbuf) {
+    p_acd = save_acd;
+  }
+
   if (try_end(err)) {
     return;
   }

src/nvim/autocmd.c

@@ -1340,7 +1340,7 @@ void aucmd_prepbuf(aco_save_T *aco, buf_T *buf)
       win_config_float(auc_win, auc_win->w_config);
     }
     // Prevent chdir() call in win_enter_ext(), through do_autochdir()
-    int save_acd = p_acd;
+    const int save_acd = p_acd;
     p_acd = false;
     // no redrawing and don't set the window title
     RedrawingDisabled++;

src/nvim/window.c

@@ -752,15 +752,20 @@ void win_set_buf(win_T *win, buf_T *buf, Error *err)
     goto cleanup;
   }
 
-  // temporarily disable 'autochdir' when using win_set_buf
-  // on non-current window
-  int save_acd = p_acd;
+  try_start();
+
+  const int save_acd = p_acd;
   if (!switchwin.sw_same_win) {
+    // Temporarily disable 'autochdir' when setting buffer in another window.
     p_acd = false;
   }
-  try_start();
+
   int result = do_buffer(DOBUF_GOTO, DOBUF_FIRST, FORWARD, buf->b_fnum, 0);
-  p_acd = save_acd;
+
+  if (!switchwin.sw_same_win) {
+    p_acd = save_acd;
+  }
+
   if (!try_end(err) && result == FAIL) {
     api_set_error(err,
                   kErrorTypeException,