Add filtering to notification channel settings

Allow apps that are launching this page to specify targeted subsets of
settings that should be shown.

Test: settings notification robotests
Bug: 177246841
Change-Id: Ib491c43f1861a9775e3b25f39134cdbe105a7ff8

src/com/android/settings/notification/app/ImportancePreferenceController.java

@@ -58,6 +58,11 @@ public class ImportancePreferenceController extends NotificationPreferenceContro
         return !isDefaultChannel();
     }
 
+    @Override
+    boolean isIncludedInFilter() {
+        return mPreferenceFilter.contains(NotificationChannel.EDIT_IMPORTANCE);
+    }
+
     @Override
     public void updateState(Preference preference) {
         if (mAppRow!= null && mChannel != null) {