bug#44521: 27.1; ivy.el breaks harfbuzz Arabic shaping

[Eli Zaretskii <eliz@gnu.org>]

> From: Thamer Mahmoud <thamer.mahmoud@gmail.com>
> Date: Sun, 08 Nov 2020 19:15:37 +0300
> 
> (progn
>   (load-library "~/.emacs.d/elpa/ivy-0.13.0/ivy-overlay.el")
>   (load-library "~/.emacs.d/elpa/ivy-0.13.0/colir.el")
>   (load-library "~/.emacs.d/elpa/ivy-0.13.0/ivy.el")
>   (ivy-mode t)
>   (run-with-timer .5 nil 'set-input-method "arabic")
>   (run-with-timer .5 nil 'insert "السلام عليكم")
>   (execute-extended-command nil))
> 
> 2. While still in the minibuffer, type any Arabic letter. Note the
>    AIN(ع) in "عليكم" changes shape from initial to final.
> 
> This bug breaks shaping in most buffers, especially after using
> swiper.el (ivy-based isearch).

I'm not familiar with ivy, but if it writes the text in the minibuffer
in several overlays, then the Arabic text will indeed become
disconnected and generally shaped incorrectly.

I'll try to look into this, but to make this easier and more efficient
I'd appreciate a test case that is less complicated, preferably not
using ivy at all.

Thanks.