bug#40774: Error messages shouldn't be hidden when the user is idle

[ndame]

>
> You want the Emacs behavior to change depending on whether "the user
> is idle" or not, right? If the practical implementation of that will
> be "when Emacs is idle", you might not have the behavior you wanted,
> because Emacs might not be idle when the user is.

If Emacs prints a message then the message function can check if the
user is idle using the same condition what run-with-idle-timer
uses and if so then it can handle displaying the message in different way.