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