Widgets recommendation backend

Add a widgets recommendation mechanism based on AiAI app predication
ranking with the following changes:

1. Only one widget is picked from one app.
2. Widgets that are already added to the workspace are excluded from
   the recommendation.

Test: run PredicationUpdateTaskTest

Bug: 179797520
Change-Id: Ia697bc6df0bae75969e68b7b3de32d57901f7461

src/com/android/launcher3/model/BaseModelUpdateTask.java

@@ -124,7 +124,7 @@ public abstract class BaseModelUpdateTask implements ModelUpdateTask {
 
     public void bindUpdatedWidgets(BgDataModel dataModel) {
         final ArrayList<WidgetsListBaseEntry> widgets =
-                dataModel.widgetsModel.getWidgetsList(mApp.getContext());
+                dataModel.widgetsModel.getWidgetsListForPicker(mApp.getContext());
         scheduleCallbackTask(c -> c.bindAllWidgets(widgets));
     }