bug#56682: Fix the long lines font locking related slowdowns

[Eli Zaretskii]

> Date: Thu, 04 Aug 2022 09:24:00 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: dgutov@yandex.ru, gerd.moellmann@gmail.com, 56682@debbugs.gnu.org, 
>     monnier@iro.umontreal.ca
> 
> I just pushed an improvement for Bidi.  I did not do so earlier because I 
> was trying to improve it further, but somehow I'm hitting a brick wall 
> here.  Could you please check, and tell me if what I already did is okay?

Hmm... which part(s) of the recent commit(s) on the branch are related
to bidi?  I only see changes related to composed characters.  What did
I miss?