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

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> IOW, the issue for which I wanted to hear your opinion was whether you
> think it's okay to preclude, in a buffer with long lines, all
> pre/post-command-hooks from accessing the entire buffer.

Yes, I think that's reasonable.  There will inevitably be many modes out
there that'll wedge themselves in the presence of gargantuan lines, and
limiting these hooks is a reasonable line of defence.