Add dismissal mechanism for contextual cards.

In the homepage, we should allow cards to be dismissed.

- Implement card flipping upon card long pressing.

Bug: 113783548
Test: robotests, visual
Change-Id: I2ddb498321ba5c5078d6944aa2ef32f1386bdb10

src/com/android/settings/homepage/contextualcards/ContextualCardController.java

@@ -28,5 +28,7 @@ public interface ContextualCardController {
 
     void onActionClick(ContextualCard card);
 
+    void onDismissed(ContextualCard card);
+
     void setCardUpdateListener(ContextualCardUpdateListener listener);
 }