bug#68213: 30.0.50; completion-preview-tests failure in --without-x build

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: Eshel Yaron <me@eshelyaron.com>,  Eli Zaretskii <eliz@gnu.org>,
>   jm@pub.pink,  68213@debbugs.gnu.org
> Date: Mon, 08 Jan 2024 14:16:54 +0800
> 
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
> 
> > But why is `mouse-4` sometimes on `mouse-wheel-down-event` and sometimes
> > on `mouse-wheel-down-alternate-event`?  What difference does it make?
> >
> > But, AFAICT the `wheel-up/down` events always mean the same, so I think
> > `mwheel.el` should just always bind `wheel-DIR` events and then the
> > `mouse-wheel-DIR-event` vars are used only for those cases where other
> > events also need to be bound, like in the patch below, WDYT?
> 
> I think we should let sleeping dogs lie, because the last time changes
> were made to these options in mwheel.el, several obscure problems
> emerged under text terminals that required another round of changes,
> yielding the current values.

There's one dog we cannot let lie: the one that fails the test in
completion-preview-tests to fail to compile -- this is what started
this bug report, and I would like to solve that problem.