bug#43383: 26.3; `toggle-menu-bar-mode-from-frame'

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: drew.adams@oracle.com,  43383@debbugs.gnu.org
> Date: Mon, 14 Sep 2020 16:51:58 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I think this command indeed has a bug, in that it cannot disable the
> > menu bar only on the frame from which it is invoked.  It _can_ enable
> > the menu bar on a single frame, see my response to Drew.  So I think
> > this command needs to be improved.  But that's another issue; the doc
> > string definitely needs to be improved.  Will you do that, or should
> > I?
> 
> Please go ahead.

Done.

I'm not closing the bug, because I think we should make the command
work according to documentation: toggle the menu bar only on the frame
from which the command is invoked.  I think it should manipulate the
menu-bar-lines frame parameter instead of invoking menu-bar mode.

Patches welcome.