bug#55387: 28.1.50; csv-mode: header does not align when line numbers are displayed

[Eli Zaretskii]

> Cc: joostkremers@fastmail.fm, 55387@debbugs.gnu.org
> Date: Fri, 13 May 2022 17:12:03 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> 
> > header-line-format would look like
> > 
> > (display-line-spaces <the rest>)
> > 
> > where display-line-spaces would indeed be updated by the redisplay code
> > (to be of the same length as (line-number-display-width 'columns)).

Btw, isn't it true that the problem is not in displaying the
header-line, but in adjusting the alignment of the _body_ of the table
to the changes in header-line (which happen automatically)?  In which
case how will header-line construct help?