Help the entity hierarchy to be a bit cleaner for `PreviousWidget`.

src/context.rs

@@ -865,20 +865,34 @@ fn update_widget(
 ) -> (Tree, bool) {
     // Check if we should update this widget
     let should_rerender = {
+        // TODO: Move the spawning to when we create the widget.  
         let old_props_entity =
             if let Ok(mut cloned_widget_entities) = cloned_widget_entities.try_write() {
-                if let Some(entity) = cloned_widget_entities.get(&entity.0).cloned() {
+                let old_parent_entity = if let Ok(tree) = tree.try_read() {
+                    if let Some(parent_entity) = tree.get_parent(entity) {
+                        cloned_widget_entities.get(&parent_entity.0).copied()
+                    } else {
+                        None
+                    }
+                } else { None };
+                if let Some(entity) = cloned_widget_entities.get(&entity.0).copied() {
                     if let Some(possible_entity) = world.get_entity(entity) {
                         let target = possible_entity.id();
                         cloned_widget_entities.insert(entity, target);
                         target
                     } else {
                         let target = world.spawn_empty().insert(PreviousWidget).id();
+                        if let Some(parent_id) = old_parent_entity {
+                            world.entity_mut(parent_id).add_child(target);
+                        }
                         cloned_widget_entities.insert(entity, target);
                         target
                     }
                 } else {
                     let target = world.spawn_empty().insert(PreviousWidget).id();
+                    if let Some(parent_id) = old_parent_entity {
+                        world.entity_mut(parent_id).add_child(target);
+                    }
                     cloned_widget_entities.insert(entity.0, target);
                     target
                 }

src/widgets/scroll/scroll_context.rs

-use bevy::prelude::{Bundle, Commands, Component, Entity, In, Query, Vec2};
+use bevy::prelude::{Bundle, Commands, Component, Entity, In, Query, Vec2, BuildChildren};
 
 use crate::{
     children::KChildren,
@@ -173,7 +173,7 @@ pub fn scroll_context_render(
     )>,
 ) -> bool {
     if let Ok((context_provider, children, styles, mut computed_styles)) = query.get_mut(entity) {
-        let context_entity = commands.spawn(context_provider.initial_value).id();
+        let context_entity = commands.spawn(context_provider.initial_value).set_parent(entity).id();
         widget_context.set_context_entity::<ScrollContext>(Some(entity), context_entity);
         *computed_styles = styles.clone().into();
         children.process(&widget_context, Some(entity));

src/widgets/window_context_provider.rs

@@ -76,7 +76,7 @@ pub fn window_context_render(
         {
             context_entity
         } else {
-            commands.spawn(WindowContext::default()).id()
+            commands.spawn(WindowContext::default()).set_parent(window_context_entity).id()
         };
         widget_context
             .set_context_entity::<WindowContext>(Some(window_context_entity), context_entity);