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

[Eli Zaretskii]

> Date: Wed, 10 Aug 2022 10:34:32 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: 56682@debbugs.gnu.org, Eli Zaretskii <eliz@gnu.org>, 
>     monnier@iro.umontreal.ca, Dmitry Gutov <dgutov@yandex.ru>
> 
> Another option might be to add some limits to the algorithm in
> buffers with long lines, without disabling it completely.

It already has such limits and other optimizations.  Inhibiting the
BPA is an option if it is known that the buffer doesn't include ant
R2L characters anywhere; otherwise some braces/parens could be
displayed incorrectly mirrored.

If you remove the 3 closing braces/brackets at EOB and the
corresponding opening braces/brackets, does navigation become
significantly faster?  These are the only brackets I could spot in the
file that enclose very large portions of text.  If removing them
doesn't help much, the only possible reason is that there are a lot of
bracketed stuff in this file.