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

[Eli Zaretskii]

> Date: Mon, 15 Aug 2022 15:06:35 +0300
> Cc: 56682@debbugs.gnu.org, gregory@heytings.org, monnier@iro.umontreal.ca
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> >> It would make sense for our defaults not to be tailored to this very
> >> particular development rig.
> > 
> > If you are willing to lose my ability to debug complex redisplay
> > problems in many cases, sure, go ahead.
> 
> Why? You would customize an option to a lower value, and go on to debugging.

I will forget to do it and waste time.

> >> syntax-propertize is general, and yet it invokes language-specific rules
> >> (through syntax-propertize-function).
> > 
> > Nothing prevents xdisp.c from invoking those same rules if needed.
> 
> True. We could basically rewrite any Lisp function we have in C 
> (font-lock-fontify-region, for example).

No need to go ad absurdum.  I was responding to your assertion that
this must be done from font-lock.