[FSD2D] Adjust backup agent creation for device-to-device migrations

1. Pass @OperationType to backup agent on creation so that it can adjust
   its behavior if needed.
2. For device-to-device migrations, always instantiate FullBackupAgent
   regardless of the app's preferences.

Bug: 160407842
Test: atest FrameworksServicesTests:ActivityManagerServiceTest
Change-Id: I89bf2b074e7a1039b9af70660a3f19a9bb7dab23