bug#42406: Mouse-wheel scrolling can be flickering

[Eli Zaretskii]

> Cc: Eli Zaretskii <eliz@gnu.org>, Alan Third <alan@idiocy.org>,
>  42406@debbugs.gnu.org
> From: martin rudalics <rudalics@gmx.at>
> Date: Thu, 17 Dec 2020 14:21:48 +0100
> 
> The (IMHO) right fix would be to have wset_update_mode_line add the
> frame containing the scrolled window to a list of frames the next
> redisplay should investigate.

That won't work without also changing redisplay_internal to consider
such a list.  It currently knows about just 2 alternatives: either
consider only the selected window on the selected frame, or all
windows on all frames -- and only the second option considers
non-window aspects (such as the frame title or menu bar) of the
selected frame.