Implement wallpaper zoom hooking it to the shade

This adds a notion of per caller wallpaper zoom, in order to support
simultaneous clients.

The shade might be pulled down while in overview, for example, and we
must coordinate between launcher and systemui.

Bug: 149792636
Bug: 146387434
Test: atest NotificationShadeWindowViewTest
Test: atest WallpaperControllerTests
Test: manual
Change-Id: I588ba56d3d2704845d033ea2a5890ce812b9ee07