Add zero state in output switcher

-Update visibility of switcher preference in SoundSetting
-Update visibility of indicator slice in Volume Panel
-Add test case

Bug: 152357002
Test: make -j50 RunSettingsRoboTests
Change-Id: I8aa4e960b72f2c3c26ced78153c4ff620a123f40

src/com/android/settings/media/MediaOutputIndicatorSlice.java

@@ -129,9 +129,9 @@ public class MediaOutputIndicatorSlice implements CustomSliceable {
         // Return true if
         // 1. AudioMode is not in on-going call
         // 2. worker is not null
-        // 3. Available devices are more than 1
+        // 3. Available devices are more than 0
         return getWorker() != null
                 && !com.android.settingslib.Utils.isAudioModeOngoingCall(mContext)
-                && getWorker().getMediaDevices().size() > 1;
+                && getWorker().getMediaDevices().size() > 0;
     }
 }