Add Cascades to the type registry, fixing lights in glTF. (#12989)

glTF files that contain lights currently panic when loaded into Bevy,
because Bevy tries to reflect on `Cascades`, which accidentally wasn't
registered.

crates/bevy_pbr/src/lib.rs

@@ -269,6 +269,7 @@ impl Plugin for PbrPlugin {
  app.register_asset_reflect::<StandardMaterial>()
  .register_type::<AmbientLight>()
  .register_type::<CascadeShadowConfig>()
+ .register_type::<Cascades>()
  .register_type::<CascadesVisibleEntities>()
  .register_type::<ClusterConfig>()
  .register_type::<CubemapVisibleEntities>()