bug#57372: no-toolkit menu popups do not respect emacs font configuration

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: tom@logand.com,  57372@debbugs.gnu.org
> Date: Wed, 24 Aug 2022 20:11:54 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Displaying pop-down menus with our display engine is "tricky", as the
> > TTY menus experience amply shows.
> 
> Indeed, though it should be easier if each pane is a separate frame.

Frames are a bad basis for menus: they (the frames) are too
heavyweight for a menu, so the resulting menus will look ugly.

And there are other issues that make this unattractive: e.g., how do
you make a frame unmovable (which is required for sub-menus)?

If we want good-looking menus independent of any toolkit, we should
try to find a small library capable of producing them on popular GUI
platforms.