Move feathers propagation into PostUpdate (#20446)

# Objective

- As discussed in
#20433 (comment),
these probably belong in `PostUpdate` to ensure that spawned objects in
`Update` have the correct values immediately without the need for
ordering.
- Finishes and closes #20356.


## Solution

- Change the schedule from `Update` to `PostUpdate`

## Testing

- I'm not sure exactly how to test this effectively: @viridia, can you
advise?

Author: alice-i-cecile

crates/bevy_feathers/src/lib.rs

@@ -18,10 +18,11 @@
 //! Please report issues, submit fixes and propose changes.
 //! Thanks for stress-testing; let's build something better together.
 
-use bevy_app::{HierarchyPropagatePlugin, Plugin, PostUpdate, Update};
+use bevy_app::{HierarchyPropagatePlugin, Plugin, PostUpdate, PropagateSet};
 use bevy_asset::embedded_asset;
-use bevy_ecs::query::With;
+use bevy_ecs::{query::With, schedule::IntoScheduleConfigs};
 use bevy_text::{TextColor, TextFont};
+use bevy_ui::UiSystems;
 use bevy_ui_render::UiMaterialPlugin;
 
 use crate::{
@@ -63,11 +64,18 @@ impl Plugin for FeathersPlugin {
         app.add_plugins((
             ControlsPlugin,
             CursorIconPlugin,
-            HierarchyPropagatePlugin::<TextColor, With<ThemedText>>::new(Update),
-            HierarchyPropagatePlugin::<TextFont, With<ThemedText>>::new(Update),
+            HierarchyPropagatePlugin::<TextColor, With<ThemedText>>::new(PostUpdate),
+            HierarchyPropagatePlugin::<TextFont, With<ThemedText>>::new(PostUpdate),
             UiMaterialPlugin::<AlphaPatternMaterial>::default(),
         ));
 
+        // This needs to run in UiSystems::Propagate so the fonts are up-to-date for `measure_text_system`
+        // and `detect_text_needs_rerender` in UiSystems::Content
+        app.configure_sets(
+            PostUpdate,
+            PropagateSet::<TextFont>::default().in_set(UiSystems::Propagate),
+        );
+
         app.insert_resource(DefaultCursor(EntityCursor::System(
             bevy_window::SystemCursorIcon::Default,
         )));