bug#71504: 30.0.50; FR: Fix suggestions ("quick fix") for Flymake diagnostics

[Eli Zaretskii <eliz@gnu.org>]

> From: Eshel Yaron <me@eshelyaron.com>
> Cc: sbaugh@janestreet.com,  71504@debbugs.gnu.org
> Date: Thu, 11 Jul 2024 09:28:35 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I'm asking what is the overall idea of the proposed implementation.  I
> > think it's worthwhile to present it, so we could see if we all agree
> > with that idea and the details of the proposed implementation.
> 
> Thanks.  To clarify, ideally Spencer will implement this feature request
> however he sees fit.  I'm offering my implementation as a reference, but
> I'm not advocating for it over other alternatives that may come up.
> 
> The idea of my implementation is to allow Flymake backends to associate
> fixes with some of the diagnostics they create, and to add a command
> that tries to apply a fix for the diagnostic at point.  For the details,
> see below the same patch I attached to this message:
> https://lists.gnu.org/archive/html/emacs-devel/2024-05/msg01318.html

Thanks.

If this is okay with Spencer, I think this should go to the master
branch, with the following two nits fixed:

  . the doc string of flymake-make-diagnostic should explicitly tell
    that :fix-function is for backends to be set to the appropriate
    fixup function
  . this is documented in flymake.texi