Move ZenModesBackend to SettingsLib.

This will allow us to access it from SystemUI.

Bug: 346519570
Test: builds
Flag: EXEMPT trivial refactor
Change-Id: I5bc480bd4eb0cbf8a26989dd11c064e66e5ee70e

src/com/android/settings/notification/modes/ZenModesFragmentBase.java

@@ -27,6 +27,7 @@ import android.provider.Settings.Global;
 import android.util.Log;
 
 import com.android.settings.dashboard.RestrictedDashboardFragment;
+import com.android.settingslib.notification.modes.ZenModesBackend;
 
 /**
  * Base class for all Settings pages controlling Modes behavior.