Enable cloning EntityHashMap and PreHashMap (#11178)

# Objective

- `EntityHashMap`, `EntityHashSet` and `PreHashMap` are currently not
Cloneable because of a missing trivial `Clone` bound for `EntityHash`
and `PreHash`. This PR makes them Cloneable.

(the parent struct `hashbrown::HashMap` requires the `HashBuilder` to be
`Clone` for the `HashMap` to be `Clone`, see:
https://github.com/rust-lang/hashbrown/blob/master/src/map.rs#L195)


## Solution

- Add a `Clone` bound to `PreHash` and `EntityHash`

---------

Co-authored-by: Charles Bournhonesque <cbournhonesque@snapchat.com>

crates/bevy_utils/src/lib.rs

@@ -189,7 +189,7 @@ impl<V: Clone, H> Clone for Hashed<V, H> {
 impl<V: Eq, H> Eq for Hashed<V, H> {}
 
 /// A [`BuildHasher`] that results in a [`PassHasher`].
-#[derive(Default)]
+#[derive(Default, Clone)]
 pub struct PassHash;
 
 impl BuildHasher for PassHash {
@@ -251,7 +251,7 @@ impl<K: Hash + Eq + PartialEq + Clone, V> PreHashMapExt<K, V> for PreHashMap<K,
 }
 
 /// A [`BuildHasher`] that results in a [`EntityHasher`].
-#[derive(Default)]
+#[derive(Default, Clone)]
 pub struct EntityHash;
 
 impl BuildHasher for EntityHash {
@@ -415,3 +415,22 @@ macro_rules! detailed_trace {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_clone_entity_hash_map() {
+        let map = EntityHashMap::<u64, usize>::default();
+        // This should compile
+        let _ = map.clone();
+    }
+
+    #[test]
+    fn test_clone_pre_hash_map() {
+        let map = PreHashMap::<u64, usize>::default();
+        // This should compile
+        let _ = map.clone();
+    }
+}