Change the ambiguity_detection test to be more strict. (#23846)

# Objective

- Fixes #23843 by preventing these systems from recurring inside Bevy.
- Note this does not fix this for users of Bevy. They would need to
setup their own "strict" checking.

## Solution

- Disable `auto_insert_apply_deferred` in the `ambiguity_detection`
example. Now these stages won't accidentally resolve these ambiguities,
so they will be detected!
- Stop running the app in `ambiguity_detection` and just manually
initialize the schedules.
- We have to do this otherwise the schedules just panic because they
depend on various resource initializations to be executed by commands
(which were previously being applied by the automatically inserted
`apply_deferred`).

### Caveats:

- The ambiguity_detection CI test now won't detect ambiguities in
runtime-added systems.
- This is not a pattern we use today, and I'd encourage us to **delete**
systems instead so that tooling can grab the systems before the app
runs.
- To clarify, this is **not** ambiguity detection in general - just
Bevy's CI test that is affected.

## Testing

- Ran the examples and all the ambiguities have been fixed in previous
PRs.

tests/ecs/ambiguity_detection.rs

@@ -35,17 +35,21 @@ fn main() {
     let sub_app = app.sub_app_mut(bevy_render::RenderApp);
     configure_ambiguity_detection(sub_app);
 
+    // Make sure all the system stuff is added.
     app.finish();
     app.cleanup();
-    app.update();
 
-    let main_app_ambiguities = count_ambiguities(app.main());
+    let main_app_ambiguities = count_ambiguities(app.main_mut());
     assert_eq!(
         main_app_ambiguities.total(),
         0,
         "Main app has unexpected ambiguities among the following schedules: \n{main_app_ambiguities:#?}.",
     );
-    let render_app_ambiguities = count_ambiguities(app.sub_app(bevy_render::RenderApp));
+
+    let render_app = app.sub_app_mut(bevy_render::RenderApp);
+    // Initialize the MainWorld so the render world systems don't fail initialization.
+    render_app.init_resource::<bevy_render::MainWorld>();
+    let render_app_ambiguities = count_ambiguities(render_app);
     assert_eq!(
         render_app_ambiguities.total(),
         0,
@@ -69,6 +73,14 @@ fn configure_ambiguity_detection(sub_app: &mut SubApp) {
         schedule.set_build_settings(ScheduleBuildSettings {
             // NOTE: you can change this to `LogLevel::Ignore` to easily see the current number of ambiguities.
             ambiguity_detection: LogLevel::Warn,
+            // With auto-inserted apply_deferred stages, these can cause two ambiguous systems to
+            // become accidentally ordered by one of the apply_deferred stages. Disabling requires
+            // us to meet a higher bar. We don't just want no ambiguities - we also don't want
+            // changes to systems or the auto-insert code from "creating" new ambiguities (by
+            // reordering the graph). However, the cost is that the graph is no longer runnable,
+            // since Bevy crates often rely on auto-insert apply_deferred to not panic (e.g.,
+            // because a resource wasn't inserted).
+            auto_insert_apply_deferred: false,
             use_shortnames: false,
             ..default()
         });
@@ -76,12 +88,23 @@ fn configure_ambiguity_detection(sub_app: &mut SubApp) {
 }
 
 /// Returns the number of conflicting systems per schedule.
-fn count_ambiguities(sub_app: &SubApp) -> AmbiguitiesCount {
-    let schedules = sub_app.world().resource::<Schedules>();
+fn count_ambiguities(sub_app: &mut SubApp) -> AmbiguitiesCount {
+    let schedule_labels = sub_app
+        .world()
+        .resource::<Schedules>()
+        .iter()
+        .map(|(_, schedule)| schedule.label())
+        .collect::<Vec<_>>();
     let mut ambiguities = <HashMap<_, _>>::default();
-    for (_, schedule) in schedules.iter() {
-        let ambiguities_in_schedule = schedule.graph().conflicting_systems().len();
-        ambiguities.insert(schedule.label(), ambiguities_in_schedule);
+    for label in schedule_labels {
+        let ambiguities_in_schedule =
+            sub_app
+                .world_mut()
+                .schedule_scope(label, |world, schedule| {
+                    schedule.initialize(world).unwrap().unwrap();
+                    schedule.graph().conflicting_systems().len()
+                });
+        ambiguities.insert(label, ambiguities_in_schedule);
     }
     AmbiguitiesCount(ambiguities)
 }