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

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@gmail.com>
> Cc: Dmitry Gutov <dgutov@yandex.ru>,  Gregory Heytings
>  <gregory@heytings.org>,  56682@debbugs.gnu.org,  Eli Zaretskii
>  <eliz@gnu.org>
> Date: Mon, 15 Aug 2022 10:10:36 +0800
> 
> > PS: Not sure if Org-mode qualifies as a mode that is likely to suffer
> > from the kinds of long-lines or large-file problems that Gregory has
> > tried to tackle, tho.  I've never seen an Org file with lines >10kB nor
> > an Org file larger than 10MB.
> 
> I have seen very long lines in Org. Specifically, in source block
> output. (http query)

How long is "very long" in those cases?