bug#50431: revert-buffer doesn't preserve read-onlyness

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Juri Linkov <juri@linkov.net>,  50431@debbugs.gnu.org
> Date: Fri, 26 Aug 2022 12:41:40 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > For that reason, I'm not sure the change that preserves the read-only
> > status across reverts is correct.  At the very least, it should be an
> > opt-in feature, IMO.
> 
> If a user has made an explicit readedness choice for a buffer, then
> preserving that over a revert is probably what they want.

Or not.  It could be an accident as well.

"Reverting" has a specific meaning: re-read the file from disk as if
it were visited anew.  If the user wants to make additional
adjustments, they will need to readjust.  I don't see why the
read-only status should be exempt from this logic.