Introduce onNotificationExpansionChanged and onNotificationDirectReplied ..

in NAS

Also, avoid the code duplication around all the notifyAssistant* methods
by pulling out the common piece of code to notifyAssistantLocked.

Bug: 111437455
Bug: 111406942

Test: Observe logs from ExtServices when a notification is expanded
      / direct replied.
Test: atest NotificationManagerServiceTest

Change-Id: I5e135d704763ecf847f82a4ff7ffe439fa56fb5c