Add isSliceable API to BasePrefController

Only support explicitly approved Settings Slices,
dictated by controllers which return true for the new
method isSliceable.

Updating the supported settings to a whitelist means that
the method to return all available slices must be updated,
and checking slicability when we index slices.

Test: robotests
Bug: 79779103
Change-Id: Ib2b9690cdd0036b5cc4a1cb846c52bce7c824ab9

src/com/android/settings/display/NightDisplayActivationPreferenceController.java

@@ -19,6 +19,7 @@ package com.android.settings.display;
 import android.content.Context;
 import androidx.preference.Preference;
 import androidx.preference.PreferenceScreen;
+import android.text.TextUtils;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;
@@ -53,6 +54,11 @@ public class NightDisplayActivationPreferenceController extends TogglePreference
         return ColorDisplayController.isAvailable(mContext) ? AVAILABLE : UNSUPPORTED_ON_DEVICE;
     }
 
+    @Override
+    public boolean isSliceable() {
+        return TextUtils.equals(getPreferenceKey(), "night_display_activated");
+    }
+
     @Override
     public void displayPreference(PreferenceScreen screen) {
         super.displayPreference(screen);