Cancel notification summary if all children were bundled before posting

 If a group summary is posted after all children were already bundled: then it should be canceled to avoid having empty summary notifications.

 This can happen if group children are posted first and bundled before the summary is posted.
 When the summary is posted, it is handled as a "summary without children" (potentially abusive notification), causing an empty summary notification to be shown.

Flag: android.service.notification.notification_classification

Test: atest NotificationManagerServiceTest
Bug: 429411981
Change-Id: I2139bdfe541f56fd6e55e072d75833c4e6bac3b0