stylecontext: Move property cache
stylecontext: Move property cache

... from per style data to only existing once per style context. This is
technically an API break because it no longer allows getting different
style properties between save()/restore() pairs, but I don't think this
was ever intended to work that way, as the style property API was to be
used and is used via gtk_widget_get_style().

And it simplifies code a lot.

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