bevy_reflect: Relax bounds on Option<T> (bevyengine#5658)

# Objective

The reflection impls on `Option<T>` have the bound `T: Reflect + Clone`. This means that using `FromReflect` requires `Clone` even though we can normally get away with just `FromReflect`.

## Solution

Update the bounds on `Option<T>` to match that of `Vec<T>`, where `T: FromReflect`. 

This helps remove a `Clone` implementation that may be undesired but added for the sole purpose of getting the code to compile.

---

## Changelog

* Reflection on `Option<T>` now has `T` bound by `FromReflect` rather than `Reflect + Clone`
* Added a `FromReflect` impl for `Instant`

## Migration Guide

If using `Option<T>` with Bevy's reflection API, `T` now needs to implement `FromReflect` rather than just `Clone`. This can be achieved easily by simply deriving `FromReflect`:

```rust

// OLD
#[derive(Reflect, Clone)]
struct Foo;

let reflected: Box<dyn Reflect> = Box::new(Some(Foo));

// NEW
#[derive(Reflect, FromReflect)]
struct Foo;

let reflected: Box<dyn Reflect> = Box::new(Some(Foo));
```
> Note: You can still derive `Clone`, but it's not required in order to compile.

crates/bevy_reflect/src/impls/std.rs

@@ -76,6 +76,7 @@ impl_from_reflect_value!(String);
 impl_from_reflect_value!(HashSet<T: Hash + Eq + Clone + Send + Sync + 'static>);
 impl_from_reflect_value!(Range<T: Clone + Send + Sync + 'static>);
 impl_from_reflect_value!(Duration);
+impl_from_reflect_value!(Instant);
 impl_from_reflect_value!(NonZeroI128);
 impl_from_reflect_value!(NonZeroU128);
 impl_from_reflect_value!(NonZeroIsize);
@@ -585,13 +586,13 @@ impl Reflect for Cow<'static, str> {
     }
 }
 
-impl<T: Reflect + Clone> GetTypeRegistration for Option<T> {
+impl<T: FromReflect> GetTypeRegistration for Option<T> {
     fn get_type_registration() -> TypeRegistration {
         TypeRegistration::of::<Option<T>>()
     }
 }
 
-impl<T: Reflect + Clone> Enum for Option<T> {
+impl<T: FromReflect> Enum for Option<T> {
     fn field(&self, _name: &str) -> Option<&dyn Reflect> {
         None
     }
@@ -655,7 +656,7 @@ impl<T: Reflect + Clone> Enum for Option<T> {
     }
 }
 
-impl<T: Reflect + Clone> Reflect for Option<T> {
+impl<T: FromReflect> Reflect for Option<T> {
     #[inline]
     fn type_name(&self) -> &str {
         std::any::type_name::<Self>()
@@ -741,7 +742,7 @@ impl<T: Reflect + Clone> Reflect for Option<T> {
 
     #[inline]
     fn clone_value(&self) -> Box<dyn Reflect> {
-        Box::new(self.clone())
+        Box::new(Enum::clone_dynamic(self))
     }
 
     fn reflect_hash(&self) -> Option<u64> {
@@ -753,7 +754,7 @@ impl<T: Reflect + Clone> Reflect for Option<T> {
     }
 }
 
-impl<T: Reflect + Clone> FromReflect for Option<T> {
+impl<T: FromReflect> FromReflect for Option<T> {
     fn from_reflect(reflect: &dyn Reflect) -> Option<Self> {
         if let ReflectRef::Enum(dyn_enum) = reflect.reflect_ref() {
             match dyn_enum.variant_name() {
@@ -762,7 +763,7 @@ impl<T: Reflect + Clone> FromReflect for Option<T> {
                         .field_at(0)
                         .expect("Field at index 0 should exist")
                         .clone_value();
-                    let field = field.take::<T>().unwrap_or_else(|_| {
+                    let field = T::from_reflect(field.as_ref()).unwrap_or_else(|| {
                         panic!(
                             "Field at index 0 should be of type {}",
                             std::any::type_name::<T>()
@@ -783,7 +784,7 @@ impl<T: Reflect + Clone> FromReflect for Option<T> {
     }
 }
 
-impl<T: Reflect + Clone> Typed for Option<T> {
+impl<T: FromReflect> Typed for Option<T> {
     fn type_info() -> &'static TypeInfo {
         static CELL: GenericTypeInfoCell = GenericTypeInfoCell::new();
         CELL.get_or_insert::<Self, _>(|| {
@@ -827,10 +828,12 @@ impl FromReflect for Cow<'static, str> {
 
 #[cfg(test)]
 mod tests {
+    use crate as bevy_reflect;
     use crate::{
-        Enum, Reflect, ReflectSerialize, TypeInfo, TypeRegistry, Typed, VariantInfo, VariantType,
+        Enum, FromReflect, Reflect, ReflectSerialize, TypeInfo, TypeRegistry, Typed, VariantInfo,
+        VariantType,
     };
-    use bevy_utils::HashMap;
+    use bevy_utils::{HashMap, Instant};
     use std::f32::consts::{PI, TAU};
 
     #[test]
@@ -939,6 +942,17 @@ mod tests {
         assert_eq!(Some(321), value);
     }
 
+    #[test]
+    fn option_should_from_reflect() {
+        #[derive(Reflect, FromReflect, PartialEq, Debug)]
+        struct Foo(usize);
+
+        let expected = Some(Foo(123));
+        let output = <Option<Foo> as FromReflect>::from_reflect(&expected).unwrap();
+
+        assert_eq!(expected, output);
+    }
+
     #[test]
     fn option_should_impl_typed() {
         type MyOption = Option<i32>;
@@ -979,4 +993,11 @@ mod tests {
         let forty_two: std::num::NonZeroUsize = crate::FromReflect::from_reflect(a).unwrap();
         assert_eq!(forty_two, std::num::NonZeroUsize::new(42).unwrap());
     }
+
+    #[test]
+    fn instant_should_from_reflect() {
+        let expected = Instant::now();
+        let output = <Instant as FromReflect>::from_reflect(&expected).unwrap();
+        assert_eq!(expected, output);
+    }
 }

crates/bevy_render/src/camera/camera.rs

@@ -19,6 +19,7 @@ use bevy_ecs::{
 };
 use bevy_math::{Mat4, UVec2, Vec2, Vec3};
 use bevy_reflect::prelude::*;
+use bevy_reflect::FromReflect;
 use bevy_transform::components::GlobalTransform;
 use bevy_utils::HashSet;
 use bevy_window::{WindowCreated, WindowId, WindowResized, Windows};
@@ -32,7 +33,7 @@ use wgpu::Extent3d;
 /// You can overlay multiple cameras in a single window using viewports to create effects like
 /// split screen, minimaps, and character viewers.
 // TODO: remove reflect_value when possible
-#[derive(Reflect, Debug, Clone, Serialize, Deserialize)]
+#[derive(Reflect, FromReflect, Debug, Clone, Serialize, Deserialize)]
 #[reflect_value(Default, Serialize, Deserialize)]
 pub struct Viewport {
     /// The physical position to render this viewport to within the [`RenderTarget`] of this [`Camera`].
@@ -71,7 +72,7 @@ pub struct ComputedCameraValues {
     target_info: Option<RenderTargetInfo>,
 }
 
-#[derive(Component, Debug, Reflect, Clone)]
+#[derive(Component, Debug, Reflect, FromReflect, Clone)]
 #[reflect(Component)]
 pub struct Camera {
     /// If set, this camera will render to the given [`Viewport`] rectangle within the configured [`RenderTarget`].

crates/bevy_time/src/time.rs

@@ -1,9 +1,9 @@
 use bevy_ecs::{reflect::ReflectResource, system::Resource};
-use bevy_reflect::Reflect;
+use bevy_reflect::{FromReflect, Reflect};
 use bevy_utils::{Duration, Instant};
 
 /// Tracks elapsed time since the last update and since the App has started
-#[derive(Resource, Reflect, Debug, Clone)]
+#[derive(Resource, Reflect, FromReflect, Debug, Clone)]
 #[reflect(Resource)]
 pub struct Time {
     delta: Duration,