bug#65536: 30.0.50; replace-regexp-in-string documentation does not mention it saves match data

[Jens Schmidt]

Not sure about this one, maybe I have overlooked something ...

The Emacs Lisp manual says:

   Notice that all functions are allowed to overwrite the match data
   unless they’re explicitly documented not to do so.

And in particular function `replace-regexp-in-string' could be
assumed to modify the match data, but it uses an explicit call to
`save-match-data' to not do so.

Maybe this should be explicitly documented in its doc string and/or
the Emacs Lisp manual ((elisp) Search and Replace) so that users of
the function can rely on that fact?