Declare "searchable" attribute for preferences.

Now we can easily mark a preference nonIndexable in xml instead of
adding key into searchIndexProvider.

Bug: 112608186
Test: robotests
Change-Id: I0ff16d44bb7b6ad148d3d35f09ca0da0163f73f4

src/com/android/settings/gestures/SwipeUpPreferenceController.java

@@ -47,6 +47,9 @@ public class SwipeUpPreferenceController extends GesturePreferenceController {
 
         final ComponentName recentsComponentName = ComponentName.unflattenFromString(
                 context.getString(R.string.config_recentsComponentName));
+        if (recentsComponentName == null) {
+            return false;
+        }
         final Intent quickStepIntent = new Intent(ACTION_QUICKSTEP)
                 .setPackage(recentsComponentName.getPackageName());
         if (context.getPackageManager().resolveService(quickStepIntent,