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

[Dmitry Gutov]

On 07.08.2022 21:38, Eli Zaretskii wrote:
> > Date: Sun, 7 Aug 2022 21:27:21 +0300
> > Cc:56682@debbugs.gnu.org,gregory@heytings.org,monnier@iro.umontreal.ca
> > From: Dmitry Gutov<dgutov@yandex.ru>
> >
> > > feel free to push a feature branch with your proposed
> > > changes, or even install them as optional features on master, and
> > > let's compare the merits and demerits of each idea in practical use
> > > cases and on a variety of systems.
> > I will.
> Thanks.

I've pushed a branch scratch/font_lock_large_files.

Please try out different values of the new variable.

Preferably test together with (setq bidi-inhibit-bpa t), to eliminate 
its contribution.