Add flag to reset notification channel importance

Add a button in development option to unlock user previously changed
notification importance and allow NAS to change the importance

Test: make RunSettingsRoboTests
Change-Id: I55b5349d6a17a383888c59b9126832c2fb8c58a0

src/com/android/settings/notification/NotificationBackend.java

@@ -585,6 +585,14 @@ public class NotificationBackend {
         sm.requestPinShortcut(shortcutInfo, null);
     }
 
+    public void resetNotificationImportance() {
+        try {
+            sINM.unlockAllNotificationChannels();
+        } catch (Exception e) {
+            Log.w(TAG, "Error calling NoMan", e);
+        }
+    }
+
     /**
      * NotificationsSentState contains how often an app sends notifications and how recently it sent
      * one.