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

[Eli Zaretskii]

> Date: Fri, 5 Aug 2022 05:03:39 +0300
> Cc: 56682@debbugs.gnu.org, Eli Zaretskii <eliz@gnu.org>,
>  monnier@iro.umontreal.ca
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> That was about a 1 GB buffer, right?
> 
> Let's take care of buffers with more reasonable sizes first, and then we 
> can consider extremes.

We want to solve all of them.

> A separate threshold for syntax-ppss to avoid parsing the whole
> buffer might fit the bill.

Don't we already have such a threshold?

But again, if you are just saying that the current balance between
response time and font-lock correctness is sub-optimal, and should be
made better by changing the values of the thresholds, that's a
different discussion.  For that discussion, we'd need a representative
enough sample of real-life files with long lines and in as many major
modes as possible, to make our balance really close to optimal.  I,
for one, will welcome more examples of such files, especially if they
use major modes we didn't consider until now.