Replace uses of gtk_css_style_get_value with direct access,
throughout the tree. We don't replace all uses, just those
where we are dealing with a fixed property. Be careful to
handle the currentColor special case for color properties.
This is a GtkRoot implemntation for drag icons,
using the surface provided by GdkDrag. This lets
us avoid GTK_WINDOW_POPUP and
gtk_window_set_hardcoded_surface.
