bug#20140: 24.4; M17n shaper output rejected

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 8 Feb 2022 22:13:10 +0000
> From: Richard Wordingham <richard.wordingham@ntlworld.com>
> Cc: larsi@gnus.org, 20140@debbugs.gnu.org, Kenichi Handa <handa@gnu.org>
> 
> On Sun, 06 Feb 2022 10:11:08 +0200
> Eli Zaretskii <eliz@gnu.org> wrote:
> 
> > I don't see the commands forward-char-intrusive and
> > backward-char-intrusive anywhere in Emacs, so I guess they are your
> > local changes, based on the code posted by Handa-san in this
> > discussion?
> 
> That's a shame; they are indeed local, sitting in my initialisation
> file (.emacs).  (I future-proofed myself too well.)  They are well worth
> adding to the general store of emacs commands, and mentioning in
> documentation next to forward-char and backward-char.

I've now added a similar feature to what will become Emacs 29 at some
future point.  The code is based on that old post by Handa-san, but I
decided to change its user-facing aspects: instead of new commands, I
added a new user option, which, if set non-nil, disables
auto-composition at point, and thus allows point to "enter" the
composed sequence.  I think this is better for 2 reasons:

  . no need to introduce new cursor motion commands, for which it will
    be hard to find a convenient key binding (using C-S-f/C-S-b will
    conflict with the shift-selection feature, for example);

  . the user option affects cursor motion by any means, so it's more
    general thus I hope will be more convenient.