bug#34513: display-line-numbers in term mode

[Eli Zaretskii]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: spacibba@aol.com, 34513@debbugs.gnu.org
> Date: Wed, 27 Feb 2019 11:40:04 -0500
> 
> How 'bout display-line-numbers-width or display-line-numbers-current-width?

I think I considered those at the time, but found them not descriptive
enough.

And please remember that originally the code was entirely in C, so
there was no "package name" to use as prefix.  display-line-numbers.el
and display-line-numbers-mode were born much later.

> >> -     (ncols (/ window-width font-width)))
> >> +     (ncols (- (/ window-width font-width) (line-number-display-width))))
> > I think you want (line-number-display-width 'columns), since this
> > wants the canonical column units, right?
> 
> Could be, I don't know.  I don't know that all callers of
> window-max-chars-per-line want that either.

I hope someone does know.