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/gestures/DoubleTapPowerPreferenceController.java

@@ -23,6 +23,7 @@ import android.content.Intent;
 import android.content.SharedPreferences;
 import android.provider.Settings;
 import androidx.annotation.VisibleForTesting;
+import android.text.TextUtils;
 
 import com.android.settings.R;
 import com.android.settings.search.DatabaseIndexingUtils;
@@ -61,6 +62,11 @@ public class DoubleTapPowerPreferenceController extends GesturePreferenceControl
         return isGestureAvailable(mContext) ? AVAILABLE : UNSUPPORTED_ON_DEVICE;
     }
 
+    @Override
+    public boolean isSliceable() {
+        return TextUtils.equals(getPreferenceKey(), "gesture_double_tap_power");
+    }
+
     @Override
     protected String getVideoPrefKey() {
         return PREF_KEY_VIDEO;