bug#33870: 27.0.50; xref-goto-xref not configurable

[Dmitry Gutov]

And also:

On 03.01.2019 3:18, Juri Linkov wrote:
>           (xref--xref-buffer-mode)
> -        (pop-to-buffer (current-buffer))
> +        (pop-to-buffer
> +         (current-buffer)
> +         `((display-buffer--maybe-same-window
> +            display-buffer-reuse-window
> +            display-buffer--maybe-pop-up-frame
> +            display-buffer-below-selected)
> +          ,(if temp-buffer-resize-mode
> +               '(window-height . resize-temp-buffer-window)
> +             '(window-height . fit-window-to-buffer))
> +          ,(when temp-buffer-resize-mode
> +             '(preserve-size . (nil . t)))))

Are we really supposed to use the private functions here, outside of 
window.el?