Fix typos in insert_or_spawn_batch/spawn_batch methods (#12812)

# Objective

- The `bundles` parameter in `insert_or_spawn_batch` method has
inconsistent naming with docs (e.g. `bundles_iter`) since #11107.

## Solution

- Replace `bundles` with `bundles_iter`, as `bundles_iter` is more
expressive to its type.

crates/bevy_ecs/src/system/commands/mod.rs

@@ -404,12 +404,12 @@ impl<'w, 's> Commands<'w, 's> {
     /// Spawning a specific `entity` value is rarely the right choice. Most apps should use [`Commands::spawn_batch`].
     /// This method should generally only be used for sharing entities across apps, and only when they have a scheme
     /// worked out to share an ID space (which doesn't happen by default).
-    pub fn insert_or_spawn_batch<I, B>(&mut self, bundles: I)
+    pub fn insert_or_spawn_batch<I, B>(&mut self, bundles_iter: I)
     where
         I: IntoIterator<Item = (Entity, B)> + Send + Sync + 'static,
         B: Bundle,
     {
-        self.queue.push(insert_or_spawn_batch(bundles));
+        self.queue.push(insert_or_spawn_batch(bundles_iter));
     }
 
     /// Pushes a [`Command`] to the queue for inserting a [`Resource`] in the [`World`] with an inferred value.
@@ -1037,13 +1037,13 @@ where
 /// A [`Command`] that consumes an iterator of [`Bundle`]s to spawn a series of entities.
 ///
 /// This is more efficient than spawning the entities individually.
-fn spawn_batch<I, B>(bundles: I) -> impl Command
+fn spawn_batch<I, B>(bundles_iter: I) -> impl Command
 where
     I: IntoIterator<Item = B> + Send + Sync + 'static,
     B: Bundle,
 {
     move |world: &mut World| {
-        world.spawn_batch(bundles);
+        world.spawn_batch(bundles_iter);
     }
 }
 
@@ -1051,13 +1051,13 @@ where
 /// If any entities do not already exist in the world, they will be spawned.
 ///
 /// This is more efficient than inserting the bundles individually.
-fn insert_or_spawn_batch<I, B>(bundles: I) -> impl Command
+fn insert_or_spawn_batch<I, B>(bundles_iter: I) -> impl Command
 where
     I: IntoIterator<Item = (Entity, B)> + Send + Sync + 'static,
     B: Bundle,
 {
     move |world: &mut World| {
-        if let Err(invalid_entities) = world.insert_or_spawn_batch(bundles) {
+        if let Err(invalid_entities) = world.insert_or_spawn_batch(bundles_iter) {
             error!(
                 "Failed to 'insert or spawn' bundle of type {} into the following invalid entities: {:?}",
                 std::any::type_name::<B>(),