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

src/com/android/settings/slices/SliceBuilderUtils.java

@@ -193,8 +193,9 @@ public class SliceBuilderUtils {
         CharSequence summaryText = controller.getSummary();
 
         // Priority 1 : User prefers showing the dynamic summary in slice view rather than static
-        // summary.
-        if (isDynamicSummaryAllowed && isValidSummary(context, summaryText)) {
+        // summary. Note it doesn't require a valid summary - so we can force some slices to have
+        // empty summaries (ex: volume).
+        if (isDynamicSummaryAllowed) {
             return summaryText;
         }