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

[Gregory Heytings]

> > But I do have similar reservations about flashing red so prominently 
> > (given that the pressing C-g does not usually indicate an error of any 
> > sort).
>
> Why not flashing the mode line with something like:

I don't understand why flashing the mode-line is among the possible 
options.  Calling the attention of the user to the mode-line is not TRT, 
it's neither where the error happened (usually at point or around point) 
nor where the error that happened is explained (in the echo area).  It's 
like flashing the fringes, there's no point in doing that when an error 
happens.

Yes, there's an option in Doom to do this.  But AFAIU Doom does that 
because it can't do better, namely, because there is no way to access the 
last error symbol in Emacs and do something with it.  This (making the 
last error symbol and data accessible from Elisp) is included in my 
proposed patch.