Separate VHAL emulator logic out.

Create EmulatedVehicleServer logic and moves emulator dependency
under it. This is part of the default VHAL refactoring. By letting
EmulatedVehicleServer depends on emulator, if we provides a
different VehicleServer implementation, it would not have emulator
dependency.

Create DefaultVehicleHal and let EmulatedVehicleHal inherits from
DefaultVehicleHal.

Test: Locally run in an emulator, test setting/getting properties
through emulator. Would add more tests in following CL.
Bug: 188204722

Change-Id: I20c4f69144277c717fed880a3bb9824f23ae0490