bug#48307: Feature request: provide default keybindings to change the font size in all windows

[Eli Zaretskii]

> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
> Date: Mon, 10 May 2021 14:34:58 -0400
> Cc: 48307@debbugs.gnu.org
> 
> Either that, or my keyboard is fast :)  Try adding (sleep-for 1) right before 
> the font size adjustment, then press "+" for a second or so and release it.  
> Emacs will keep processing the delayed "+" input and keep zooming.

I don't think that Emacs can know when the user stopped pressing the
keys.  Without that, how can we know when to discard keypresses still
in the queue.