Update SoundSettings to extend DashboardFragment.

- initial round of refactoring SoundSettings to use DashboardFragment.
- add controller for Cast, Do not disturb, Alarm volume, Media volume,
  Ring volume and Notification volume.

Bug: 32276590
Test: make RunSettingsRoboTests
Change-Id: I5c02a344bff5117bfce93d7ccac650fccc82d2b0

src/com/android/settings/notification/VolumeSeekBarPreference.java

@@ -146,7 +146,9 @@ public class VolumeSeekBarPreference extends SeekBarPreference {
     @Override
     public void onProgressChanged(SeekBar seekBar, int progress, boolean fromTouch) {
         super.onProgressChanged(seekBar, progress, fromTouch);
-        mCallback.onStreamValueChanged(mStream, progress);
+        if (mCallback != null) {
+            mCallback.onStreamValueChanged(mStream, progress);
+        }
     }
 
     private void updateIconView() {