Ranker --> Assistant.

Rename ranker to assistant and make some of the methods public.
Delete the ext services ranker and restore the listener-type
lifecycle to the assistant.

Test: manual. add a notification assistant and verify it gets
assistant and listener callbacks.

Change-Id: Ia3406c8c14d923426c1b8a6d8b5187efe64c31c3
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 4eebea6..f3b513d 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -2937,11 +2937,11 @@
         android:protectionLevel="signature" />
 
     <!-- Must be required by an {@link
-         android.service.notification.NotificationRankerService         to ensure that only the system can bind to it.
+         android.service.notification.NotificationAssistantService to ensure that only the system
+         can bind to it.
          <p>Protection level: signature
-         @hide This is not a third-party API (intended for system apps). -->
     -->
-    <permission android:name="android.permission.BIND_NOTIFICATION_RANKER_SERVICE"
+    <permission android:name="android.permission.BIND_NOTIFICATION_ASSISTANT_SERVICE"
         android:protectionLevel="signature" />
 
     <!-- Must be required by a {@link