Create a scene from a dynamic scene (#6229)

# Objective

- Add a method to create a `Scene` from a `DynamicScene`

crates/bevy_scene/src/dynamic_scene.rs

@@ -50,14 +50,15 @@ impl DynamicScene {
     /// Write the dynamic entities and their corresponding components to the given world.
     ///
     /// This method will return a [`SceneSpawnError`] if a type either is not registered
-    /// or doesn't reflect the [`Component`](bevy_ecs::component::Component) trait.
-    pub fn write_to_world(
+    /// in the provided [`AppTypeRegistry`] resource, or doesn't reflect the
+    /// [`Component`](bevy_ecs::component::Component) trait.
+    pub fn write_to_world_with(
         &self,
         world: &mut World,
         entity_map: &mut EntityMap,
+        type_registry: &AppTypeRegistry,
     ) -> Result<(), SceneSpawnError> {
-        let registry = world.resource::<AppTypeRegistry>().clone();
-        let type_registry = registry.read();
+        let type_registry = type_registry.read();
 
         for scene_entity in &self.entities {
             // Fetch the entity with the given entity id from the `entity_map`
@@ -99,6 +100,20 @@ impl DynamicScene {
         Ok(())
     }
 
+    /// Write the dynamic entities and their corresponding components to the given world.
+    ///
+    /// This method will return a [`SceneSpawnError`] if a type either is not registered
+    /// in the world's [`AppTypeRegistry`] resource, or doesn't reflect the
+    /// [`Component`](bevy_ecs::component::Component) trait.
+    pub fn write_to_world(
+        &self,
+        world: &mut World,
+        entity_map: &mut EntityMap,
+    ) -> Result<(), SceneSpawnError> {
+        let registry = world.resource::<AppTypeRegistry>().clone();
+        self.write_to_world_with(world, entity_map, &registry)
+    }
+
     // TODO: move to AssetSaver when it is implemented
     /// Serialize this dynamic scene into rust object notation (ron).
     pub fn serialize_ron(&self, registry: &TypeRegistryArc) -> Result<String, ron::Error> {

crates/bevy_scene/src/scene.rs

@@ -6,7 +6,7 @@ use bevy_ecs::{
 };
 use bevy_reflect::TypeUuid;
 
-use crate::{InstanceInfo, SceneSpawnError};
+use crate::{DynamicScene, InstanceInfo, SceneSpawnError};
 
 /// To spawn a scene, you can use either:
 /// * [`SceneSpawner::spawn`](crate::SceneSpawner::spawn)
@@ -25,6 +25,18 @@ impl Scene {
         Self { world }
     }
 
+    /// Create a new scene from a given dynamic scene.
+    pub fn from_dynamic_scene(
+        dynamic_scene: &DynamicScene,
+        type_registry: &AppTypeRegistry,
+    ) -> Result<Scene, SceneSpawnError> {
+        let mut world = World::new();
+        let mut entity_map = EntityMap::default();
+        dynamic_scene.write_to_world_with(&mut world, &mut entity_map, type_registry)?;
+
+        Ok(Self { world })
+    }
+
     /// Clone the scene.
     ///
     /// This method will return a [`SceneSpawnError`] if a type either is not registered in the