New Pipeline: Extend the NotifPipeline to include a render stage with callbacks

* RenderStageManager implements the pipeline behavior for handoff and listeners.
* ViewRenderer interface (implemented by ShadeViewManager) defines view update API.
* Implement a StackCoordinator (and similar logic in NotificationViewHierarchyManager) which sets notification stats on the NotifStackController rather than letting this be calculated by the view.  This is an example conversion to unidirectional data flow.

Bug: 204674942
Test: atest NotifPipelineTest PreparationCoordinatorTest NodeSpecBuilderTest RenderStageManagerTest StackCoordinatorTest GroupCountCoordinatorTest

Change-Id: I7b2296504202a9cbe87d5d3ead9bd3afffa00aab