Add Volume panel

Volume panel hosts each volume stream, including:
- Media volume
- Call Volume
- Ring volume
- Alarm volume

Change-Id: I1801d10d2304c57615e9499386c638c74ffcd7c3
Screenshot: https://screenshot.googleplex.com/m764j65ECto
Bug: 117804161
Test: Manual app
Test: robolectric

tests/robotests/src/com/android/settings/slices/SliceBuilderUtilsTest.java

@@ -217,6 +217,19 @@ public class SliceBuilderUtilsTest {
         assertThat(summary).isEqualTo(controllerSummary);
     }
 
+    @Test
+    public void getDynamicSummary_allowDynamicSummary_nullSummary_returnsNull() {
+        final SliceData data = getDummyData(true /*isDynamicSummaryAllowed*/);
+        final FakePreferenceController controller = spy(
+                new FakePreferenceController(mContext, KEY));
+        final String controllerSummary = null;
+        doReturn(controllerSummary).when(controller).getSummary();
+
+        final CharSequence summary = SliceBuilderUtils.getSubtitleText(mContext, controller, data);
+
+        assertThat(summary).isNull();
+    }
+
     @Test
     public void getDynamicSummary_returnsScreenTitle() {
         final SliceData data = getDummyData();