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

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Gerd Möllmann <gerd.moellmann@gmail.com>,
>   56682@debbugs.gnu.org,
>   gregory@heytings.org,  visuweshm@gmail.com
> Date: Sun, 24 Jul 2022 10:36:41 -0400
> 
> > redisplay are different.  When we find one such interval, it is
> > guaranteed to have changes only in the text properties that are of
> > interest to redisplay, but the search could take more time if there
> > are many text properties that are not interesting, because there are
> > more intervals to check.
> 
> Not only more intervals, but also more elements in the `plist`s of
> each interval.

Could be, if there are many different properties.  But since we are
talking about font-lock, there's only one we are talking about:
'face'.