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

[Lars Ingebrigtsen]

Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs@gnu.org> writes:

> `face` may be the one we care about, but there will be others
> (especially in the case you were talking about, i.e. the impact of
> non-display-related faces)

Random thought: Would it make sense to make `put-text-property' (and
friends) try to ensure that `face' (and `font-lock-face'?) are towards
the start of the plists?

That wouldn't help with intervals that don't have a `face' at all, but
should speed up the ones that have, and would be relatively low impact.

I don't think we guarantee anything about the order, so it might not
break anything.