Support device without desktop wallpaper

This CL adds consideration for devices which don’t have desktop
wallpaper (i.e., show widgets even in desktop session).
Please note that `tapl.launchedAppState` expects any fullscreen app is
visible and `tapl.workspace` expects no fullscreen app is visible.

Flag: EXEMPT - test fix
Bug: 416610249
Test: ConnectedDisplayCujSmokeTests

Change-Id: Icd38410dc7e8257da44f033c120d044a4a55482d