bug#55668: Extending the `C-x 8' map to include macrons

[Eli Zaretskii <eliz@gnu.org>]

> From: Tor Kringeland <tor.kringeland@ntnu.no>
> Date: Fri, 27 May 2022 01:03:10 +0000
> 
> I suggest chaning the `C-x 8' to add macrons to letters after `C-x 8 -'
> and move the current `C-x 8 -' to `C-x 8 - -'.  Something similar was
> done a while ago with `C-x 8 .' being moved to `C-x 8 . .' to allow for
> new character compositions.

I _really_ don't like us changing the default key bindings that exist
for a significant amount of time.  "C-x 8 -" exists at least since
Emacs 22, so changing it would be a bad blow to people's habits.

It sounds like you want to search for letters with combining macron,
like ā and ō?  If so, why not use a suitable input method to type
those letters?  That is the standard way in Emacs to type characters
that are not on the keyboard.  (If support for typing those characters
is missing from the input methods we have, we could relatively easily
add them.)

> (It could be said that `C-x 8 _' be used, but it already has an entry
> for `C-x 8 _ o' and it's not `ō'.)

We could augment iso-transl.el to produce the likes of ā via "C-x 8",
e.g. with "C-x 8 a -" or "C-x 8 a _".