bug#69511: Restore any state after revert-buffer

[Juri Linkov <juri@linkov.net>]

close 69511 30.0.50
thanks

> One of numerous examples is to save and restore
> hidden outlines after doing 'revert-buffer':
>
> (add-hook 'Buffer-menu-mode-hook
>           (lambda ()
>             (add-hook 'revert-buffer-state-functions
>                       (lambda ()
>                         (let ((regexp (outline-hidden-headings-regexp)))
>                           (when regexp
>                             (lambda ()
>                               (outline-hide-by-heading-regexp regexp))))))))
>
> Currently this handles outlines only in the buffer list.
> But probably this settings should be added to outline-minor-mode.

This is now adapted to outline-minor-mode.
(xref needs changes as well, so the patch is sent to bug#49731).

> And here is the immediate need to use it to rehighlight the outlines
> after reverting the buffer list:
>
> diff --git a/lisp/buff-menu.el b/lisp/buff-menu.el
> +  (add-hook 'tabulated-list-revert-hook 'list-buffers--refresh nil t)
> +  (add-hook 'revert-buffer-state-functions
> +            (lambda ()
> +              (when (bound-and-true-p outline-minor-mode)
> +                (lambda ()
> +                  (outline-minor-mode-highlight-buffer))))))

And this was moved to outline-minor-mode as well.