Add ability to clear all components on an entity via EntityWorldMut (#13588)

# Objective

Adds capability to clear all components on an entity without de-spawning
said entity.

## Testing

The function calls `remove_by_id` on every component in the entity
archetype - wasn't sure if it's worth going out of our way to create a
test for this considering `remove_by_id` is already unit tested.

---

## Changelog

Added `clear` function to `EntityWorldMut` which removes all components
on an entity.

## Migration Guide

N/A

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

crates/bevy_ecs/src/system/commands/mod.rs

@@ -1011,6 +1011,11 @@ impl EntityCommands<'_> {
         self.add(remove_by_id(component_id))
     }
 
+    /// Removes all components associated with the entity.
+    pub fn clear(&mut self) -> &mut Self {
+        self.add(clear())
+    }
+
     /// Despawns the entity.
     ///
     /// See [`World::despawn`] for more details.
@@ -1237,6 +1242,15 @@ fn remove_by_id(component_id: ComponentId) -> impl EntityCommand {
     }
 }
 
+/// An [`EntityCommand`] that removes all components associated with a provided entity.
+fn clear() -> impl EntityCommand {
+    move |entity: Entity, world: &mut World| {
+        if let Some(mut entity) = world.get_entity_mut(entity) {
+            entity.clear();
+        }
+    }
+}
+
 /// An [`EntityCommand`] that removes components from an entity.
 /// For a [`Bundle`] type `T`, this will remove all components except those in the bundle.
 /// Any components in the bundle that aren't found on the entity will be ignored.

crates/bevy_ecs/src/world/entity_ref.rs

@@ -1178,6 +1178,22 @@ impl<'w> EntityWorldMut<'w> {
         self
     }
 
+    /// Removes all components associated with the entity.
+    pub fn clear(&mut self) -> &mut Self {
+        let component_ids: Vec<ComponentId> = self.archetype().components().collect();
+        let components = &mut self.world.components;
+
+        let bundle_id = self
+            .world
+            .bundles
+            .init_dynamic_info(components, component_ids.as_slice());
+
+        // SAFETY: the `BundleInfo` for this `component_id` is initialized above
+        self.location = unsafe { self.remove_bundle(bundle_id) };
+
+        self
+    }
+
     /// Despawns the current entity.
     ///
     /// See [`World::despawn`] for more details.