Add scoped overlay hosts

tests/color_space.rs

@@ -30,7 +30,7 @@ fn solid_paints_and_images_round_trip_through_an_srgb_target() {
         .span(Dir::RIGHT)
         .add_strong(&mut harness.rsc)
         .any();
-    harness.state.set_root(root);
+    harness.state.set_root(&mut harness.rsc, root);
     harness.frame(0);
 
     let mut renderer =