Log whether a notification has a summary

This may be with the NOTIFICATION_POSTED event (seems to be what I see in practice with the tester) but also can be posted afterwards with an adjustment, as summaries are already included in the diff that merits logging.

Flag: android.app.nm_summarization_ui
Bug: 409751981
Test: NotificationManagerServiceTest, atom tester
Change-Id: Id088c62835da98d1d49e2a0ebfdebc81b2ce7f5a