Use ZenModesBackend for tile state

Also had to move TestModeBuilder to SettingsLib so we can use it in
tests here too.

Bug: 346519570
Test: tested manually that tile state gets updated when toggling dnd&bedtime
Flag: android.app.modes_ui

Change-Id: Ib85e2ede102f98cc5ebde714734aa976c3e1f9e4
7 files changed