More fixes for display-comint-buffer-action

* lisp/window.el (display-comint-buffer-action):
Use display-buffer--same-window-action as the default value.

* lisp/progmodes/sh-script.el (sh-show-shell):
* lisp/shell.el (shell): Add display-comint-buffer-action to pop-to-buffer.

* lisp/progmodes/project.el (project-shell, project-eshell): Use
`bound-and-true-p display-comint-buffer-action' for backward-compatibility.

https://lists.gnu.org/archive/html/emacs-devel/2021-12/msg02964.html

lisp/progmodes/project.el

@@ -1017,7 +1017,7 @@ if one already exists."
          (default-project-shell-name (project-prefixed-buffer-name "shell"))
          (shell-buffer (get-buffer default-project-shell-name)))
     (if (and shell-buffer (not current-prefix-arg))
-        (pop-to-buffer shell-buffer display-comint-buffer-action)
+        (pop-to-buffer shell-buffer (bound-and-true-p display-comint-buffer-action))
       (shell (generate-new-buffer-name default-project-shell-name)))))
 
 ;;;###autoload
@@ -1033,7 +1033,7 @@ if one already exists."
          (eshell-buffer-name (project-prefixed-buffer-name "eshell"))
          (eshell-buffer (get-buffer eshell-buffer-name)))
     (if (and eshell-buffer (not current-prefix-arg))
-        (pop-to-buffer eshell-buffer display-comint-buffer-action)
+        (pop-to-buffer eshell-buffer (bound-and-true-p display-comint-buffer-action))
       (eshell t))))
 
 ;;;###autoload

lisp/progmodes/sh-script.el

@@ -1407,7 +1407,7 @@ If FORCE is non-nil and no process found, create one."
 (defun sh-show-shell ()
   "Pop the shell interaction buffer."
   (interactive)
-  (pop-to-buffer (process-buffer (sh-shell-process t))))
+  (pop-to-buffer (process-buffer (sh-shell-process t)) display-comint-buffer-action))
 
 (defun sh-send-text (text)
   "Send the text to the `sh-shell-process'."

lisp/shell.el

@@ -758,7 +758,7 @@ Make the shell buffer the current buffer, and return it.
                  (current-buffer)))
   ;; The buffer's window must be correctly set when we call comint
   ;; (so that comint sets the COLUMNS env var properly).
-  (pop-to-buffer buffer)
+  (pop-to-buffer buffer display-comint-buffer-action)
 
   (with-connection-local-variables
    ;; On remote hosts, the local `shell-file-name' might be useless.

lisp/window.el

@@ -7474,7 +7474,7 @@ ALIST.  See `display-buffer' for details."
   :version "24.1"
   :group 'windows)
 
-(defcustom display-comint-buffer-action '((display-buffer-same-window))
+(defcustom display-comint-buffer-action display-buffer--same-window-action
   "`display-buffer' action for displaying comint buffers."
   :type display-buffer--action-custom-type
   :risky t