do not impl Component for Task (#4113)

# Objective

- `Task` are `Component`.
- They should not.

## Solution

- Remove the impl, and update the example to show a wrapper.

#4052 for reference

crates/bevy_ecs/src/component.rs

@@ -55,14 +55,6 @@ mod sealed {
     impl Sealed for super::SparseStorage {}
 }
 
-// ECS dependencies cannot derive Component, so we must implement it manually for relevant structs.
-impl<T> Component for bevy_tasks::Task<T>
-where
-    Self: Send + Sync + 'static,
-{
-    type Storage = TableStorage;
-}
-
 /// The storage used for a specific component type.
 ///
 /// # Examples

examples/async_tasks/async_compute.rs

@@ -43,6 +43,9 @@ fn add_assets(
     commands.insert_resource(BoxMaterialHandle(box_material_handle));
 }
 
+#[derive(Component)]
+struct ComputeTransform(Task<Transform>);
+
 /// This system generates tasks simulating computationally intensive
 /// work that potentially spans multiple frames/ticks. A separate
 /// system, `handle_tasks`, will poll the spawned tasks on subsequent
@@ -66,7 +69,7 @@ fn spawn_tasks(mut commands: Commands, thread_pool: Res<AsyncComputeTaskPool>) {
                 });
 
                 // Spawn new entity and add our new task as a component
-                commands.spawn().insert(task);
+                commands.spawn().insert(ComputeTransform(task));
             }
         }
     }
@@ -78,12 +81,12 @@ fn spawn_tasks(mut commands: Commands, thread_pool: Res<AsyncComputeTaskPool>) {
 /// removes the task component from the entity.
 fn handle_tasks(
     mut commands: Commands,
-    mut transform_tasks: Query<(Entity, &mut Task<Transform>)>,
+    mut transform_tasks: Query<(Entity, &mut ComputeTransform)>,
     box_mesh_handle: Res<BoxMeshHandle>,
     box_material_handle: Res<BoxMaterialHandle>,
 ) {
     for (entity, mut task) in transform_tasks.iter_mut() {
-        if let Some(transform) = future::block_on(future::poll_once(&mut *task)) {
+        if let Some(transform) = future::block_on(future::poll_once(&mut task.0)) {
             // Add our new PbrBundle of components to our tagged entity
             commands.entity(entity).insert_bundle(PbrBundle {
                 mesh: box_mesh_handle.clone(),
@@ -93,7 +96,7 @@ fn handle_tasks(
             });
 
             // Task is complete, so remove task component from entity
-            commands.entity(entity).remove::<Task<Transform>>();
+            commands.entity(entity).remove::<ComputeTransform>();
         }
     }
 }