GTK3: Back port Wayland fixes from the GTK4 code. Wayland can't draw to a widget outside of an expose event. Any attempts to draw to a widget outside of an expose will mark the widget as dirty. Calling dw_flush() will trigger expose events on all dirty widgets. On X11 draw directly as we used to do, dirty list should remain empty. This will allow code written with the assumption we can draw any time to function. In the future, design code to only draw in the expose callback.