Add onActionClicked in NotificationAssistantService

This is added to report clicks on actions buttons to NAS.

BUG: 119010281
Test: atest SystemUITests
Test: atest RemoteViewsTest
Test: atest NotificationManagerServiceTest
Test: Manual. Tapped on the action (both normal and contextual) and
      observed the log.

Change-Id: I381994737d8c3185d3fabf9b6c481fd01a89a634