bug#54564: 29.0.50; [PATCH] Use gsettings font rendering entries for pgtk builds

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: pieter.van.prooijen@teloden.nl,  54564@debbugs.gnu.org
> Date: Sat, 26 Mar 2022 14:44:53 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Does the below fit the bill?
> >
> >    clear_face_cache (true);
> >
> > Or did you mean to do this only on a single frame (or on specific
> > selected frames)?  Then looking inside clear_face_cache will tell you
> > how to do that.
> 
> It should be done for each frame on every display, so clear_face_cache
> probably does fit the bill.  (Though perhaps clear_font_cache on each
> window system frame by itself will be enough?)

Actually, I see that clear_face_cache doesn't force clearing of the
font cache on every frame, only those frames which have "enough" fonts
defined.  So I guess an explicit call to clear_font_cache for every
frame, followed by free_all_realized_faces, will be needed.