SysUI/NoMan: Log clicks on notification buttons

Introduce notification_action_click logtag that is logged whenever
the user clicks any notification button. For standard templates, we
also log the index of the pressed action button.

Bug: 18064190
Change-Id: Icb07795ff711729d16bde0b7e03d13c2f466779c
diff --git a/services/core/java/com/android/server/EventLogTags.logtags b/services/core/java/com/android/server/EventLogTags.logtags
index 64d8f6f..f7925f0 100644
--- a/services/core/java/com/android/server/EventLogTags.logtags
+++ b/services/core/java/com/android/server/EventLogTags.logtags
@@ -69,6 +69,8 @@
 27511 notification_expansion (key|3),(user_action|1),(expanded|1)
 # when a notification has been clicked
 27520 notification_clicked (key|3)
+# when a notification action button has been clicked
+27521 notification_action_clicked (key|3),(action_index|1)
 
 # ---------------------------
 # Watchdog.java