Fix compatibility with polymode after pm--visible-buffer-name removal

Replace pm--visible-buffer-name with pm--buffer-name to maintain
compatibility with polymode commit 32d0d6d which removed the
pm--visible-buffer-name function and replaced it with pm--buffer-name.

The pm--buffer-name function takes an optional 'hidden parameter:
- pm--buffer-name() returns the visible buffer name (equivalent to old pm--visible-buffer-name)
- pm--buffer-name('hidden) returns the hidden buffer name (equivalent to old pm--hidden-buffer-name)

This change fixes the issue where ein would fail to load due to the
undefined pm--visible-buffer-name function.

Fixes compatibility with polymode >= commit 32d0d6d.

Author: natsirtguy

lisp/poly-ein.el

@@ -351,13 +351,13 @@ TYPE can be \\='body, nil."
                   (apply-partially #'poly-ein--narrow-to-inner #'identity))))
 
 (defun poly-ein--record-window-buffer ()
-  "(pm--visible-buffer-name) needs to get onto window's prev-buffers.
+  "(pm--buffer-name) needs to get onto window's prev-buffers.
 But `C-x b` seems to consult `buffer-list' and not the C (window)->prev_buffers."
   (when (buffer-base-buffer)
     (let* ((buffer-list (frame-parameter nil 'buffer-list))
            (pos-visible (seq-position
                          buffer-list
-                         (pm--visible-buffer-name)
+                         (pm--buffer-name)
                          (lambda (x visible*)
                            (string-prefix-p (buffer-name x) visible*)))))
       ;; no way to know if i've switched in or out of indirect buf.
@@ -382,7 +382,7 @@ But `C-x b` seems to consult `buffer-list' and not the C (window)->prev_buffers.
   (add-hook 'ido-make-buffer-list-hook
 	    (lambda ()
 	      (defvar ido-temp-list)
-	      (when-let ((visible (pm--visible-buffer-name)))
+	      (when-let ((visible (pm--buffer-name)))
 		(ido-to-end (delq nil
 				  (mapcar (lambda (x)
 					    (when (string-prefix-p x visible) x))