Updated JsonConfigLoader to parse access for area configs

If access is populated in VehicleAreaConfig, access field will remain
empty in VehiclePropConfig.

Updated VHAL layer tests to test new access mode granularity logic

Added new tests and modified others in JsonConfigLoaderUnitTest to test
new parsing logic.

Added VTS test to enforce exclusively one of VehiclePropConig.access and
the VehicleAreaConfig.access fields are populated.

Bug: 290801790
Test: atest JsonConfigLoaderUnitTest
Test: atest VtsHalAutomotiveVehicle_TargetTest
Change-Id: I6cc4f20c289141123d3e2093e45084109fbf4d9d