Add CommunalHostView.

This changelist introduces CommunalHostView, a parent
container for hosting communal content on the lockscreen
UI. This ViewGroup eases managing the positioning and
visibility of communal-related content. An associated
controller for managing the view and dependency
associations have also been added.

Bug: 193550437
Test: atest CommunalHostViewControllerTest
Change-Id: Ifbf3784a065cdceb6708bde0bd17b578874f904f