bug#43926: 26.3; Face `header-line-highlight': inherit from `mode-line-highlight', not `highlight'

[Eli Zaretskii]

> Date: Sun, 11 Oct 2020 08:55:12 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> 
> I'd also suggest that `mode-line-highlight' inherit from `highlight' (in
> addition to its current default attribute settings).

You want to have this face display as both raised-button _and_
highlighted in color?  Which other applications do something like
that?

Where the 3D face is not available, we do inherit from 'highlight'.