Add BaseControllerV2 support to ComposableController (#447)

The ComposableController now supports controllers that are based upon
BaseControllerV2. These newer controllers use the controller messaging
system to communicate, so the messenger is now a required constructor
parameter if any BaseControllerV2 controllers are used.

The `name` property in `BaseControllerV2` had to be made public for the
ComposableController to properly construct its state. This seems OK. It
was only kept private initially until a use was found for it.

src/BaseControllerV2.ts

@@ -129,7 +129,12 @@ export class BaseController<
     string | never
   >;
 
-  private name: N;
+  /**
+   * The name of the controller.
+   *
+   * This is used by the ComposableController to construct a composed application state.
+   */
+  public readonly name: N;
 
   public readonly metadata: StateMetadata<S>;