NotificationKind not exported

[cartant]

Bug Report

Current Behavior

6.4.0 introduced a const enum: NotificationKind. However, that enum is not exported:

/* Notification */
export { Notification } from './internal/Notification';

That means that it's not possible to create a Notification instance (without resorting to an as any assertion).

This was a breaking change for me, as the tests for rxjs-spy need to be able to create Notification instances. (It's also a breaking change because current calls to the constructor - like new Notification("N", "alice") - are now invalid.)