bug#70784: Abolish string resizing

[Eli Zaretskii]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Sun, 26 May 2024 05:02:01 -0400
> Cc: 70784@debbugs.gnu.org, monnier@iro.umontreal.ca
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I'm not sure even that is a good idea for Emacs 30.
> >
> > Let's see what others think.
> 
> Is there any drawback to adding a warning?

A nuisance, obviously, for something that was valid code for eons.

> It seems like it would help Emacs package developers, not all of
> which track master.

I'd be happier if we waited with this till Emacs 31.  This will let
people more time to see the change and react to it, if they want.