Add explicit orthogonal span sizing

tests/unsettled.rs

@@ -173,6 +173,7 @@ fn plant_pair(h: &mut Harness, swapped: bool) -> (Vec<WidgetId>, WeakWidget<Span
         children,
         dir: Dir::RIGHT,
         gap: 0.0,
+        ortho: OrthoSize::Children,
     }
     .add(&mut h.rsc);
     let span_handle = span;
@@ -230,6 +231,7 @@ fn plant_scrolled(h: &mut Harness, swapped: bool) -> (Vec<WidgetId>, [WeakWidget
         children: inner_children,
         dir: Dir::RIGHT,
         gap: 0.0,
+        ortho: OrthoSize::Children,
     }
     .add(&mut h.rsc);
     let block = rect(Color::RED).add(&mut h.rsc);
@@ -248,6 +250,7 @@ fn plant_scrolled(h: &mut Harness, swapped: bool) -> (Vec<WidgetId>, [WeakWidget
         children: outer_children,
         dir: Dir::RIGHT,
         gap: 0.0,
+        ortho: OrthoSize::Children,
     }
     .add(&mut h.rsc);
     let through = SetSize {