Add log to NoMan for canceled cancels

In the case where a notification_cancel is skipped when finding a more
recently enqueued notification for the same key, now throw a log so we
know that we're dropping a message from the system.

Bug: 162652224
Test: manual
Change-Id: I313076f8b15b00286f532ace1bbe7da2f7db4afe

services/core/java/com/android/server/notification/NotificationManagerService.java

@@ -6259,6 +6259,8 @@ public class NotificationManagerService extends SystemService {
                     for (NotificationRecord r : enqueued) {
                         if (r.mUpdateTimeMs > mWhen) {
                             // At least one enqueue was posted after the cancel, so we're invalid
+                            Slog.i(TAG, "notification cancel ignored due to newer enqueued entry"
+                                    + "key=" + r.getSbn().getKey());
                             return;
                         }
                     }