bevy_reflect: IntoIter for DynamicList and DynamicMap (#4108)

# Objective

In some cases, you may want to take ownership of the values in `DynamicList` or `DynamicMap`. 

I came across this need while trying to implement a custom deserializer, but couldn't get ownership of the values in the list.

## Solution

Implemented `IntoIter` for both `DynamicList` and `DynamicMap`.

crates/bevy_reflect/src/list.rs

@@ -191,6 +191,15 @@ impl<'a> Iterator for ListIter<'a> {
     }
 }
 
+impl IntoIterator for DynamicList {
+    type Item = Box<dyn Reflect>;
+    type IntoIter = std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.values.into_iter()
+    }
+}
+
 impl<'a> ExactSizeIterator for ListIter<'a> {}
 
 /// Applies the elements of `b` to the corresponding elements of `a`.
@@ -244,3 +253,21 @@ pub fn list_partial_eq<L: List>(a: &L, b: &dyn Reflect) -> Option<bool> {
 
     Some(true)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::DynamicList;
+
+    #[test]
+    fn test_into_iter() {
+        let mut list = DynamicList::default();
+        list.push(0usize);
+        list.push(1usize);
+        list.push(2usize);
+        let items = list.into_iter();
+        for (index, item) in items.into_iter().enumerate() {
+            let value = item.take::<usize>().expect("couldn't downcast to usize");
+            assert_eq!(index, value);
+        }
+    }
+}

crates/bevy_reflect/src/map.rs

@@ -220,6 +220,15 @@ impl<'a> Iterator for MapIter<'a> {
     }
 }
 
+impl IntoIterator for DynamicMap {
+    type Item = (Box<dyn Reflect>, Box<dyn Reflect>);
+    type IntoIter = std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.values.into_iter()
+    }
+}
+
 impl<'a> ExactSizeIterator for MapIter<'a> {}
 
 /// Compares a [`Map`] with a [`Reflect`] value.
@@ -253,3 +262,28 @@ pub fn map_partial_eq<M: Map>(a: &M, b: &dyn Reflect) -> Option<bool> {
 
     Some(true)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::DynamicMap;
+
+    #[test]
+    fn test_into_iter() {
+        let expected = vec!["foo", "bar", "baz"];
+
+        let mut map = DynamicMap::default();
+        map.insert(0usize, expected[0].to_string());
+        map.insert(1usize, expected[1].to_string());
+        map.insert(2usize, expected[2].to_string());
+
+        for (index, item) in map.into_iter().enumerate() {
+            let key = item.0.take::<usize>().expect("couldn't downcast to usize");
+            let value = item
+                .1
+                .take::<String>()
+                .expect("couldn't downcast to String");
+            assert_eq!(index, key);
+            assert_eq!(expected[index], value);
+        }
+    }
+}