bevy_reflect: Add Reflect::into_reflect (#6502)

# Objective

Using `Reflect` we can easily switch between a specific reflection trait object, such as a `dyn Struct`, to a `dyn Reflect` object via `Reflect::as_reflect` or `Reflect::as_reflect_mut`.

```rust
fn do_something(value: &dyn Reflect) {/* ... */}

let foo: Box<dyn Struct> = Box::new(Foo::default());
do_something(foo.as_reflect());
```

However, there is no way to convert a _boxed_ reflection trait object to a `Box<dyn Reflect>`.

## Solution

Add a `Reflect::into_reflect` method which allows converting a boxed reflection trait object back into a boxed `Reflect` trait object.

```rust
fn do_something(value: Box<dyn Reflect>) {/* ... */}

let foo: Box<dyn Struct> = Box::new(Foo::default());
do_something(foo.into_reflect());
```

---

## Changelog

- Added `Reflect::into_reflect`

Author: MrGVSV

crates/bevy_reflect/bevy_reflect_derive/src/impls/enums.rs

@@ -202,6 +202,11 @@ pub(crate) fn impl_enum(reflect_enum: &ReflectEnum) -> TokenStream {
                 self
             }
 
+            #[inline]
+            fn into_reflect(self: Box<Self>) -> Box<dyn #bevy_reflect_path::Reflect> {
+                self
+            }
+
             #[inline]
             fn as_reflect(&self) -> &dyn #bevy_reflect_path::Reflect {
                 self

crates/bevy_reflect/bevy_reflect_derive/src/impls/structs.rs

@@ -183,6 +183,11 @@ pub(crate) fn impl_struct(reflect_struct: &ReflectStruct) -> TokenStream {
                 self
             }
 
+            #[inline]
+            fn into_reflect(self: Box<Self>) -> Box<dyn #bevy_reflect_path::Reflect> {
+                self
+            }
+
             #[inline]
             fn as_reflect(&self) -> &dyn #bevy_reflect_path::Reflect {
                 self

crates/bevy_reflect/bevy_reflect_derive/src/impls/tuple_structs.rs

@@ -145,6 +145,11 @@ pub(crate) fn impl_tuple_struct(reflect_struct: &ReflectStruct) -> TokenStream {
                 self
             }
 
+            #[inline]
+            fn into_reflect(self: Box<Self>) -> Box<dyn #bevy_reflect_path::Reflect> {
+                self
+            }
+
             #[inline]
             fn as_reflect(&self) -> &dyn #bevy_reflect_path::Reflect {
                 self

crates/bevy_reflect/bevy_reflect_derive/src/impls/values.rs

@@ -64,6 +64,11 @@ pub(crate) fn impl_value(meta: &ReflectMeta) -> TokenStream {
                 self
             }
 
+            #[inline]
+            fn into_reflect(self: Box<Self>) -> Box<dyn #bevy_reflect_path::Reflect> {
+                self
+            }
+
             #[inline]
             fn as_reflect(&self) -> &dyn #bevy_reflect_path::Reflect {
                 self

crates/bevy_reflect/src/array.rs

@@ -197,6 +197,11 @@ impl Reflect for DynamicArray {
         self
     }
 
+    #[inline]
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     #[inline]
     fn as_reflect(&self) -> &dyn Reflect {
         self

crates/bevy_reflect/src/enums/dynamic_enum.rs

@@ -315,6 +315,11 @@ impl Reflect for DynamicEnum {
         self
     }
 
+    #[inline]
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     #[inline]
     fn as_reflect(&self) -> &dyn Reflect {
         self

crates/bevy_reflect/src/impls/smallvec.rs

@@ -90,6 +90,10 @@ where
         self
     }
 
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     fn as_reflect(&self) -> &dyn Reflect {
         self
     }

crates/bevy_reflect/src/impls/std.rs

@@ -245,6 +245,10 @@ impl<T: FromReflect> Reflect for Vec<T> {
         self
     }
 
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     fn as_reflect(&self) -> &dyn Reflect {
         self
     }
@@ -413,6 +417,11 @@ impl<K: FromReflect + Eq + Hash, V: FromReflect> Reflect for HashMap<K, V> {
         self
     }
 
+    #[inline]
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     fn as_reflect(&self) -> &dyn Reflect {
         self
     }
@@ -543,6 +552,11 @@ impl<T: Reflect, const N: usize> Reflect for [T; N] {
         self
     }
 
+    #[inline]
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     #[inline]
     fn as_reflect(&self) -> &dyn Reflect {
         self
@@ -661,6 +675,10 @@ impl Reflect for Cow<'static, str> {
         self
     }
 
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     fn as_reflect(&self) -> &dyn Reflect {
         self
     }
@@ -819,6 +837,11 @@ impl<T: FromReflect> Reflect for Option<T> {
         self
     }
 
+    #[inline]
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     fn as_reflect(&self) -> &dyn Reflect {
         self
     }

crates/bevy_reflect/src/lib.rs

@@ -989,6 +989,21 @@ mod tests {
         }
     }
 
+    #[test]
+    fn into_reflect() {
+        trait TestTrait: Reflect {}
+
+        #[derive(Reflect)]
+        struct TestStruct;
+
+        impl TestTrait for TestStruct {}
+
+        let trait_object: Box<dyn TestTrait> = Box::new(TestStruct);
+
+        // Should compile:
+        let _ = trait_object.into_reflect();
+    }
+
     #[test]
     fn as_reflect() {
         trait TestTrait: Reflect {}

crates/bevy_reflect/src/list.rs

@@ -216,6 +216,11 @@ impl Reflect for DynamicList {
         self
     }
 
+    #[inline]
+    fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
+        self
+    }
+
     #[inline]
     fn as_reflect(&self) -> &dyn Reflect {
         self