Update accessibility for popup

- Content description includes count of notifications.
- Notifications have a dismiss action.
- All icons that support shortcuts will have action to show
  shortcut menu, since there will be system shortcuts even if
  there are no deep shortcuts.

Bug: 36564782
Change-Id: I51b085fa26754f2dcd93c7db6548f2edf054f494

src/com/android/launcher3/notification/NotificationFooterLayout.java

@@ -141,6 +141,7 @@ public class NotificationFooterLayout extends FrameLayout {
         icon.setBackground(info.getIconForBackground(getContext(), mBackgroundColor));
         icon.setOnClickListener(info);
         icon.setTag(info);
+        icon.setImportantForAccessibility(IMPORTANT_FOR_ACCESSIBILITY_NO);
         mIconRow.addView(icon, 0, mIconLayoutParams);
         return icon;
     }