bug#33007: 27.0.50; Proposal for function to edit and return string

[Drew Adams <drew.adams@oracle.com>]

> Don't we already have something like that in Customize
> and/or in EWW, where they allow the user to fill fields
> in a form?

As Michael said, " I think it already has been reinvented
multiple times in Emacs itself."

The buffer is usually exited with `C-c C-c'. If the buffer
contains Lisp code, that's typically read with `read'
when you use `C-c C-c'.

The mode should be configurable, maybe defaulting
to Emacs Lisp mode (?). A key (other than `q') should
let you cancel (burying or killing the buffer without
evaluating or otherwise processing it in any way).

The functions that (1) create and display the buffer
and (2) process it (e.g. a command bound to `C-c C-c',
by default) or cancel it should be usable in various
ways, for buffer content of various kinds and for
processing of various kinds.

This should be done as simply as possible, e.g. as
contrasted with something like what `view-mode'
does, which is complex. If we want to provide
different buffer-display behaviors that should be
done simply somehow.