Add DiffCallback to handle Contextual Cards update.

Use DiffCallback in ContextualCardsAdapter to only update items that
are changed instead of touching those unchanged ones.

Also fix a bug where ConditionContexualCardCard#onStart is incorrectly
skipped.

Fixes: 112245748
Bug: 118165942
Test: robotests
Change-Id: I7989d621764fe40a3fceb8c9f40baced840818ba

src/com/android/settings/homepage/conditional/ConditionManager.java

@@ -107,12 +107,12 @@ public class ConditionManager {
      */
     public void startMonitoringStateChange() {
         if (mIsListeningToStateChange) {
-            Log.d(TAG, "Already listening to condition state changes, skipping");
-            return;
-        }
-        mIsListeningToStateChange = true;
-        for (ConditionalCardController controller : mCardControllers) {
-            controller.startMonitoringStateChange();
+            Log.d(TAG, "Already listening to condition state changes, skipping monitor setup");
+        } else {
+            mIsListeningToStateChange = true;
+            for (ConditionalCardController controller : mCardControllers) {
+                controller.startMonitoringStateChange();
+            }
         }
         // Force a refresh on listener
         onConditionChanged();