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

[Eli Zaretskii]

> Date: Fri, 5 Aug 2022 14:34:12 +0300
> Cc: gregory@heytings.org, 56682@debbugs.gnu.org, monnier@iro.umontreal.ca
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> We really have different problems and thus need different solutions for 
> them. Not just one blunt instrument.

The current opinion of both the head maintainers and of Gregory is
that these are all parts of the same problem, and a single class of
solutions can solve most of them.  The problem being that many
portions of Emacs code involved in navigation and redisplay don't
expect lines to be too long, and therefore employ algorithms that
don't scale well with line length.  Preventing such code from going
far back to the beginning of the previous line, and then coming back
through all that text, is therefore an idea that should appear very
reasonable.  It also works surprisingly well in practice, at least
according to what we know at this point.

I get it that you disagree, but I haven't seen any real data behind
your dissenting opinions, and thus I don't yet see any reason to
reconsider changing the direction of development in this regard.