star-image: Transition between two icons

This replaces the custom drawing of a star by partially drawing a starred and a non-starred icon. This not only makes the code simpler, but it follows the GTK 4 recommendations of replacing custom drawings by widgets and CSS. This fixes deprecations in GTK 4.10 as gtk_snapshot_render_frame() is going away. This also allows us to more easily use more complex and different shapes, by using one icon for the starred part and another for the non-starred part.

Before

After