Use different pip shadow for each tv pip menu mode

This is the first of several CLs addressing the shadow on the tv pip
menu. In this CL we add a dedicated class TvPipBackgroundView for the
view hierarchy in the background surface of the Tv Pip menu. This
view is responsible for drawing the shadow behind the Tv PiP window.

The TvPipBackgroundView will be using a different shadow intensity for
each of the TvPipMenuModes. In this CL we adjust the shadow only using
the View translationZ attribute

Bug: 220108601
Test: atest TvPipMenuControllerTests
Change-Id: If191c4fac4a977f4678e59848aec2be6a2375e75