Remove all existing file notification watches from Emacs

[Michael Albinus]

While working on bug#51146, I found the following command useful, which
removes all file notification watches from an Emacs instance:

--8<---------------cut here---------------start------------->8---
(defun file-notify-rm-all-watches ()
  "Remove all existing file notification watches from Emacs."
  (interactive)
  (maphash
   (lambda (key _value)
     (file-notify-rm-watch key))
   file-notify-descriptors))
--8<---------------cut here---------------end--------------->8---

The code is simple enough to avoid regressions. I'd like to add it to
the emacs-28 branch (plus doc), any objection?

Best regards, Michael.