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

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Cc: Eli Zaretskii <eliz@gnu.org>,
>       "56682@debbugs.gnu.org" <56682@debbugs.gnu.org>,
>       "monnier@iro.umontreal.ca" <monnier@iro.umontreal.ca>
> Date: Fri, 12 Aug 2022 19:35:57 +0300
> 
> I have eliminated two performance problems frim js-json-mode that are 
> uncharacteristic for font-lock in
> general. One used a pathological matcher (simply removed), and another uses 
> the "frameworks" facility
> which simply always rescans the full buffer from the beginning. That one 
> can/should be fixed later, but I have
> disabled it for JSON (where it doesn't make sense anyway).
> 
> You should know that the rest of js-mode's font-lock keywords are still 
> there. I experimented with leaving just
> the bare minimum needed for JSON, but the effect was very minimal (like 20% 
> improvement).

I didn't yet have time to try the branch, but what you say begs a
question: does the branch attempt to solve the problems of JSON files
only, or does it attempt to solve a more general problem?