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

[Eli Zaretskii]

> Cc: gerd.moellmann@gmail.com, 56682@debbugs.gnu.org, monnier@iro.umontreal.ca,
>  dgutov@yandex.ru
> Date: Thu, 04 Aug 2022 17:14:58 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> 
> > Date: Thu, 04 Aug 2022 10:33:48 +0000
> > From: Gregory Heytings <gregory@heytings.org>
> > cc: gerd.moellmann@gmail.com, 56682@debbugs.gnu.org, 
> > monnier@iro.umontreal.ca, 
> >     dgutov@yandex.ru
> > 
> > navigating through the locales.json file was slow (at some positions) 
> > before the change and is now reasonably fast (but alas not instantaneous).
> 
> Which navigation commands were slow, as compared to the same commands
> in other portions of this file?

Just before the Devanagari portion of the file, there's the Hebrew
portion, starting around buffer position 3243400.  If you go there and
try the same navigation commands that were slow with Arabic, are they
as slow with Hebrew (which is also a right-to-left script, but doesn't
use character compositions nearly as heavily as Arabic)?  Here it
looks like Hebrew is noticeably faster, as fast as Devanagari.