icontheme: Add some more tests
icontheme: Add some more tests

This test checks that gtk_icon_theme_list_icons and
gtk_icon_theme_has_icon work as expected.

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