bug#42865: 28.0.50; Add new 'copy-region-quietly' defcustom

[Juri Linkov]

> I think we'd have to introduce a new function, like...
>
> (defun information (name &rest args)
>   (when (information-wanted name)
>     (apply #'message args)))
>
> that would allow inhibiting messages based on names and or levels

This looks like the existing function 'user-error' that
doesn't enter the debugger when 'debug-on-error' is t.
Does the name 'user-message' make more sense?

But the problem is that it would be a huge endeavor
to replace all 'message' calls with a new function call.

So maybe a better route is to add a list of ignored messages like
'debug-ignored-errors' contains a list of regexps that match messages
to ignore.

Then this will disable display of the copy-region message:

  (add-to-list 'ignored-messages "^Saved text")