bug#51094: Check if run-with{-idle, }-timer needs to create a timer

[Eli Zaretskii]

> Cc: 51094@debbugs.gnu.org
> Date: Fri, 08 Oct 2021 11:46:00 +0100
> From:  "Basil L. Contovounesios" via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Philip Kaludercic [2021-10-08 09:36 +0000] wrote:
> 
> > I have seen a few packages use run-with-timer or run-with-idle-timer,
> > where the SECS parameter is configurable with a user option. When this
> > timer doesn't repeat itself and it makes sense to set SECS to 0 when you
> > want something to run immediately, I don't think it makes sense to
> > create a timer object.
> 
> IIUC, the semantics of SECS=0 (alias nil) is not the same as eager
> funcall, because timer functions are intended to be run asynchronously
> in a separate command loop.  So often what is meant by "now" is e.g. "as
> soon as I quit the current active minibuffer".

Right, and that's one more aspect of this change to consider.  It
could very well change the behavior in incompatible ways, so I wonder
whether we really should make this change.