Move 'show hidden channels' option

Make it more prominent to make it more clear what's happening
when you unblock an app

Test: DeletedChannelsPreferenceControllerTest
Test: ShowMorePreferenceControllerTest
Flag: com.android.server.notification.notification_hide_unused_channels
Bug: 322536537
Change-Id: I745b2037b4dc907a4307fa7f70ecc3a4c9db2dd2

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

@@ -16,6 +16,8 @@
 
 package com.android.settings.notification.app;
 
+import static com.android.server.notification.Flags.notificationHideUnusedChannels;
+
 import android.content.Context;
 
 import androidx.preference.Preference;
@@ -44,6 +46,9 @@ public class DeletedChannelsPreferenceController extends NotificationPreferenceC
         if (!super.isAvailable()) {
             return false;
         }
+        if (notificationHideUnusedChannels()) {
+            return false;
+        }
         // only visible on app screen
         if (mChannel != null || hasValidGroup()) {
             return false;