Add device state request APIs to DeviceStateManager.

This change promotes DeviceStateManager to a TestApi and exposes three
additional methods:
- getSupportedStates: returns a list of state ids that can be used with
requestState().
- submitRequest: requests that the device enter the supplied state.
- cancelRequest: clears the current requested device state.
to be used initially in CTS tests.

Bug: 177235528
Bug: 177236115
Test: atest DeviceStateManagerServiceTest
Test: atest DeviceStateManagerGlobalTest

Change-Id: Ieae9208420ddecea641a5c44f1610d3cb7071b07