Controls API - New method for suggested controls

Add a defaulted method, loadSuggestedControls(), in order to ask an
application for controls to suggest to the user. The idea is that OEMs
can choose a default application, and seed the controls area with a
small number of controls that may be helpful to the user.

Bug: 149037812
Test: atest ControlsProviderServiceTest
Change-Id: Icf9638c2d07988519527c24383693c4b9e0bb6d3