bug#1305: All code that currently beeps should use visual bell instead

[Eli Zaretskii]

> Date: Sun, 18 Apr 2021 17:02:35 +0000
> From: Gregory Heytings <gregory@heytings.org>
> Cc: Michael Welsh Duggan <mwd@md5i.com>, jasonspiro4@gmail.com,
>  1305@debbugs.gnu.org, Stefan Kangas <stefan@marxist.se>,
>  monnier@iro.umontreal.ca
> 
> > I think, perhaps, introducing a new visible bell (across all significant 
> > system), that's considerably less intrusive than the ones we have today 
> > on GNU/Linux and Macos, might be an option.  And then defaulting to 
> > using that.
> >
> > Gregory suggested blinking the cursor in a different colour -- perhaps?
> >
> 
> I attach a POC of what I have in mind.

If this is being proposed as the default setting, then we should have
a different default for TTY frames, because AFAIR cursor color cannot
be changed there, right?

>   (sit-for 0.5)

I think half a second is too long, a bell should be much shorter, like
0.1 sec or something.