bug#57669: 29.0.50; C-n, C-p off under long lines

[Eli Zaretskii]

> Cc: 57669@debbugs.gnu.org
> From: dick <dick.r.chiang@gmail.com>
> Date: Fri, 09 Sep 2022 10:34:28 -0400
> 
> > Try the same with a buffer with 10 lines, each of which is 10 MB long.
> 
> I don't have the patience for 10MB.  How about 0.1MB?
> 
> OUTPUT:
> 
> Under long-line-threshold=nil find-file ineffable
> Under long-line-threshold=10000 find-file 99s

This means on average 1 sec per C-n.  Which is tolerable.

> Under long-line-threshold=nil find-file-literally ineffable
> Under long-line-threshold=10000 find-file-literally 8s

We know that visiting a file literally makes this much faster, but it
also loses a lot of features that we prefer not to lose.  Like display
of non-ASCII characters, for example.