Add VTS test for timestamp for AIDL backend.

The expected behavior for timestamp was not clearly defined in HIDL.
In AIDL, we add clearer definition based on the existing HIDL ref
impl's behavior. This CL add VTS test to enforce these behavior for
AIDL backend.

Test: atest VtsHalAutomotiveVehicle_TargetTest
Bug: 225191802
Change-Id: Ic208d6ac20cb7b820249c9b545c7b3a83528a1dd