Post the FGS notification for the FGS delegation

If the caller of the delegation has set the notification in the options,
we'll post the notification as a FGS notification. If it's not set,
then the FGS delegation will be running as FGS state without a
notification, which is a legacy behavior since Android U.

Bug: 295518668
Test: atest CtsAppTestCases:ActivityManagerFgsDelegateTest
Test: atest FrameworksMockingServicesTests:ActivityManagerServiceTest
Change-Id: Ib57ddbd98724921de8a09220a9cb4ef1ec595e08