Added new properties on Vehicle HAL to support user management.

These initial properties are:

- INITIAL_USER_INFO: gets information about the initial user, it will
  replace the android.car.systemuser.bootuseroverrideid system property
  approach.
- SWITCH_USER_REQUEST: used to communicate a user switch request from
  Android to HAL, or vice versa.

This CL only defines the new types, they're not implemented or used yet.

Test: m -j android.hardware.automotive.vehicle@2.0-service
Bug: 146207078

Change-Id: I25055f8adc90aaebaf3a3faa9a9b73c284440624