switch to Rc<RefCell<...>> for widget storage

src/core/position/scroll.rs

@@ -1,7 +1,7 @@
 use crate::prelude::*;
 
 pub struct Scroll {
-    inner: WidgetId,
+    inner: WidgetRef,
     axis: Axis,
     amt: f32,
     snap_end: bool,
@@ -41,7 +41,7 @@ impl Widget for Scroll {
 }
 
 impl Scroll {
-    pub fn new(inner: WidgetId, axis: Axis) -> Self {
+    pub fn new(inner: WidgetRef, axis: Axis) -> Self {
         Self {
             inner,
             axis,