Redesign span layout around retained placement

src/widget/position/layer.rs

@@ -10,6 +10,8 @@ impl Widget for LayerOffset {
         for _ in 0..self.offset {
             painter.next_layer();
         }
-        painter.widget(&self.inner)
+        let used = painter.widget(&self.inner);
+        painter.place_used(&self.inner, used, UiRegion::FULL);
+        used
     }
 }