bug#47712: 27.1; Provide `string-display-width` function, which takes properties into account, `substring-width`

[Eli Zaretskii]

> Cc: 47712@debbugs.gnu.org
> From: martin rudalics <rudalics@gmx.at>
> Date: Tue, 13 Apr 2021 09:06:06 +0200
> 
> (defun string-pixel-width (string)
>    (let ((buffer (get-buffer-create "*foo*"))
>       (old-buffer (window-buffer)))
>      (with-current-buffer buffer
>        (erase-buffer)
>        (insert string)
>        (set-window-buffer (selected-window) buffer)
>        (prog1
>         (window-text-pixel-size nil (point-min) (point-max))
>       (set-window-buffer (selected-window) old-buffer)))))

Thanks.  This produces correct results, and takes 35-37 usec per call
here.