bug#53636: 29.0.50; face-remapping broken on master

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 53636@debbugs.gnu.org,  tsdh@gnu.org
> Date: Thu, 03 Feb 2022 20:24:03 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Anyway, what I was thinking of is a really simple solution: Have
> >> `face-remap-add-relative' loop over all children and remap them, too.
> >
> > That'd mean looping over all the known faces for each change in
> > face-remapping-alist, wouldn't it?  Because we don't track which faces
> > inherit from a given face, we can only tell the reverse: from which
> > faces a given face inherits.
> 
> Yes, but the number of faces is pretty small

No, it isn't.  We had examples with hundreds of faces, back when we
decided to store faces in a hash-table.