bug#54371: 29.0.50; read-char does not reset idle timer in some cases

[Eli Zaretskii]

> From: Ignacio Casso <ignaciocasso@hotmail.com>
> Cc: Lars Ingebrigtsen <larsi@gnus.org>, 54371@debbugs.gnu.org
> Date: Sun, 13 Mar 2022 18:45:33 +0100
> 
> However, I still think that if not a bug, this is at least inconsistent
> and probably deserving a footnote in the relevant section of the Emacs
> Lisp manual
> (https://www.gnu.org/software/emacs/manual/html_node/elisp/Idle-Timers.html).

I think accessing current-idle-time from an idle time is inherently
problematic: when the idle timer runs and receives input, whether or
not Emacs is idle is ambiguous in principle.  IOW, code which does
that is splitting hair.