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

[Eli Zaretskii]

> Date: Sat, 17 Apr 2021 12:31:27 +0000
> From: Gregory Heytings <gregory@heytings.org>
> Cc: jasonspiro4@gmail.com, 1305@debbugs.gnu.org,
>  Stefan Kangas <stefan@marxist.se>, Stefan Monnier <monnier@iro.umontreal.ca>
> 
> IMO, the default behavior on GNU/Linux (inverting video on the first and 
> last line of the frame) is horrible (but perhaps less so than an actual 
> bell), and the default behavior on macOS is too intrusive (but again 
> perhaps less so than an actual bell).

On MS-Windows, we use a system API that flashes the caption bar of the
selected-frame's window.