Add remove method to Map reflection trait. (#6564)

# Objective

- Implements removal of entries from a `dyn Map`
- Fixes #6563

## Solution

- Adds a `remove` method to the `Map` trait which takes in a `&dyn Reflect` key and returns the value removed if it was present.

---

## Changelog

- Added `Map::remove`

## Migration Guide

- Implementors of `Map` will need to implement the `remove` method.


Co-authored-by: radiish <[email protected]>

Author: soqb

crates/bevy_reflect/src/impls/std.rs

@@ -394,6 +394,17 @@ impl<K: FromReflect + Eq + Hash, V: FromReflect> Map for HashMap<K, V> {
         self.insert(key, value)
             .map(|old_value| Box::new(old_value) as Box<dyn Reflect>)
     }
+
+    fn remove(&mut self, key: &dyn Reflect) -> Option<Box<dyn Reflect>> {
+        let mut from_reflect = None;
+        key.downcast_ref::<K>()
+            .or_else(|| {
+                from_reflect = K::from_reflect(key);
+                from_reflect.as_ref()
+            })
+            .and_then(|key| self.remove(key))
+            .map(|value| Box::new(value) as Box<dyn Reflect>)
+    }
 }
 
 impl<K: FromReflect + Eq + Hash, V: FromReflect> Reflect for HashMap<K, V> {

crates/bevy_reflect/src/map.rs

@@ -57,6 +57,12 @@ pub trait Map: Reflect {
         key: Box<dyn Reflect>,
         value: Box<dyn Reflect>,
     ) -> Option<Box<dyn Reflect>>;
+
+    /// Removes an entry from the map.
+    ///
+    /// If the map did not have this key present, `None` is returned.
+    /// If the map did have this key present, the removed value is returned.
+    fn remove(&mut self, key: &dyn Reflect) -> Option<Box<dyn Reflect>>;
 }
 
 /// A container for compile-time map info.
@@ -246,6 +252,14 @@ impl Map for DynamicMap {
         }
     }
 
+    fn remove(&mut self, key: &dyn Reflect) -> Option<Box<dyn Reflect>> {
+        let index = self
+            .indices
+            .remove(&key.reflect_hash().expect(HASH_ERROR))?;
+        let (_key, value) = self.values.remove(index);
+        Some(value)
+    }
+
     fn drain(self: Box<Self>) -> Vec<(Box<dyn Reflect>, Box<dyn Reflect>)> {
         self.values
     }