Add IntoIterator impls for &Query and &mut Query (#4692)

# Objective

These types of IntoIterator impls are a common pattern in Rust, and these implementations make this common pattern work for bevy queries.

Author: TheRawMeatball

crates/bevy_ecs/src/system/mod.rs

@@ -925,4 +925,19 @@ mod tests {
         assert!(entity.contains::<A>());
         assert!(entity.contains::<B>());
     }
+
+    #[test]
+    fn into_iter_impl() {
+        let mut world = World::new();
+        world.spawn().insert(W(42u32));
+        run_system(&mut world, |mut q: Query<&mut W<u32>>| {
+            for mut a in &mut q {
+                assert_eq!(a.0, 42);
+                a.0 = 0;
+            }
+            for a in &q {
+                assert_eq!(a.0, 0);
+            }
+        });
+    }
 }

crates/bevy_ecs/src/system/query.rs

@@ -1129,6 +1129,24 @@ impl<'w, 's, Q: WorldQuery, F: WorldQuery> Query<'w, 's, Q, F> {
     }
 }
 
+impl<'w, 's, Q: WorldQuery, F: WorldQuery> IntoIterator for &'w Query<'_, 's, Q, F> {
+    type Item = ROQueryItem<'w, Q>;
+    type IntoIter = QueryIter<'w, 's, Q, ROQueryFetch<'w, Q>, F>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<'w, Q: WorldQuery, F: WorldQuery> IntoIterator for &'w mut Query<'_, '_, Q, F> {
+    type Item = QueryItem<'w, Q>;
+    type IntoIter = QueryIter<'w, 'w, Q, QueryFetch<'w, Q>, F>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
 /// An error that occurs when retrieving a specific [`Entity`]'s component from a [`Query`]
 #[derive(Debug)]
 pub enum QueryComponentError {