expose ambiguities of ScheduleGraph (#7716)

# Objective

- other tools (bevy_mod_debugdump) would like to have access to the ambiguities so that they can do their own reporting/visualization

## Solution

- store `conflicting_systems` in `ScheduleGraph` after calling `build_schedule`

The solution isn't very pretty and as pointed out it #7522, there may be a better way of exposing this, but this is the quick and dirty way if we want to have this functionality exposed in 0.10.

crates/bevy_ecs/src/schedule/schedule.rs

@@ -234,6 +234,11 @@ impl Schedule {
         &self.graph
     }
 
+    /// Returns a mutable reference to the [`ScheduleGraph`].
+    pub fn graph_mut(&mut self) -> &mut ScheduleGraph {
+        &mut self.graph
+    }
+
     /// Iterates the change ticks of all systems in the schedule and clamps any older than
     /// [`MAX_CHANGE_AGE`](crate::change_detection::MAX_CHANGE_AGE).
     /// This prevents overflow and thus prevents false positives.
@@ -377,6 +382,7 @@ pub struct ScheduleGraph {
     ambiguous_with: UnGraphMap<NodeId, ()>,
     ambiguous_with_flattened: UnGraphMap<NodeId, ()>,
     ambiguous_with_all: HashSet<NodeId>,
+    conflicting_systems: Vec<(NodeId, NodeId, Vec<ComponentId>)>,
     changed: bool,
     settings: ScheduleBuildSettings,
     default_base_set: Option<BoxedSystemSet>,
@@ -398,6 +404,7 @@ impl ScheduleGraph {
             ambiguous_with: UnGraphMap::new(),
             ambiguous_with_flattened: UnGraphMap::new(),
             ambiguous_with_all: HashSet::new(),
+            conflicting_systems: Vec::new(),
             changed: false,
             settings: default(),
             default_base_set: None,
@@ -500,6 +507,14 @@ impl ScheduleGraph {
         &self.dependency
     }
 
+    /// Returns the list of systems that conflict with each other, i.e. have ambiguities in their access.
+    ///
+    /// If the `Vec<ComponentId>` is empty, the systems conflict on [`World`] access.
+    /// Must be called after [`ScheduleGraph::build_schedule`] to be non-empty.
+    pub fn conflicting_systems(&self) -> &[(NodeId, NodeId, Vec<ComponentId>)] {
+        &self.conflicting_systems
+    }
+
     fn add_systems<P>(&mut self, systems: impl IntoSystemConfigs<P>) {
         let SystemConfigs { systems, chained } = systems.into_configs();
         let mut system_iter = systems.into_iter();
@@ -1149,6 +1164,7 @@ impl ScheduleGraph {
                 return Err(ScheduleBuildError::Ambiguity);
             }
         }
+        self.conflicting_systems = conflicting_systems;
 
         // build the schedule
         let dg_system_ids = self.dependency_flattened.topsort.clone();