GtkSettings: Consider default settings for font hinting and antialias
GtkSettings: Consider default settings for font hinting and antialias

Arrange things so that gtk-xdg-hinting==-1 and gtk-xfg-antialias==-1
end up as CAIRO_HINT_STYLE_DEFAULT and CAIRO_ANTIALIAS_DEFAULT in the
cairo font options.

This will not change anything on Linux desktops where xsettings will
always provide values different from -1. But on other platforms, we
can benefit from getting the platform-specific defaults in cairo.

Based on the first patch in:
https://bugzilla.gnome.org/show_bug.cgi?id=735316

jadahl/gtk,jigpu/gtk,jadahl/gtk,Lyude/gtk-,davidgumberg/gtk,jadahl/gtk,Adamovskiy/gtk,jigpu/gtk,chergert/gtk,jigpu/gtk,Lyude/gtk-,Adamovskiy/gtk,Lyude/gtk-,Adamovskiy/gtk,alexlarsson/gtk,jadahl/gtk,ahodesuka/gtk,alexlarsson/gtk,chergert/gtk,davidgumberg/gtk,grubersjoe/adwaita,grubersjoe/adwaita,chergert/gtk,jadahl/gtk,jadahl/gtk,Adamovskiy/gtk,Adamovskiy/gtk,alexlarsson/gtk,ahodesuka/gtk,alexlarsson/gtk,Adamovskiy/gtk,Lyude/gtk-,grubersjoe/adwaita,davidgumberg/gtk,davidgumberg/gtk,Lyude/gtk-,Lyude/gtk-,Adamovskiy/gtk,ahodesuka/gtk,ahodesuka/gtk,grubersjoe/adwaita,davidgumberg/gtk,jigpu/gtk,chergert/gtk,jadahl/gtk,Lyude/gtk-,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,alexlarsson/gtk,ahodesuka/gtk,jigpu/gtk,ahodesuka/gtk,Lyude/gtk-,alexlarsson/gtk,davidgumberg/gtk,jigpu/gtk,jadahl/gtk,Adamovskiy/gtk,grubersjoe/adwaita,chergert/gtk,chergert/gtk,grubersjoe/adwaita,ahodesuka/gtk,grubersjoe/adwaita,chergert/gtk,alexlarsson/gtk,alexlarsson/gtk,jigpu/gtk,jigpu/gtk,ahodesuka/gtk,davidgumberg/gtk