Lock screen LWP: use WallpaperService for lock screen.

Uses a second WallpaperService for the lock screen when lock and home
wallpapers are different. This supports static and live wallpapers for
either screen.

CTS tests pass for with lock screen LWP enabled and disabled. They will
be merged after visibility issues are resolved.

Bug: 253507223
Test: atest WallpaperManagerTest
Change-Id: I2483e3a0808f3a61598fb87e69eb582df24a3daf