Publish when communal view is occluded.

This changelist pipes the proper signals through
the CommunalHostViewController to notify the
CommunalStateController when the communal view is
occluded. Currently, this applies when the shade
(notification or QS) is brought over the communal
view.

Bug: 196889682
Test: atest CommunalHostViewControllerTest#testReportOcclusion
Change-Id: Ic0fbe837b0a2fdcad8dfcb13c83a7444542cd84a