Added VehicleHal.dump()

This (optional) function allows the HAL implementation customize lshal debug;
for example, it could:
  - augment dump() by dumping its own state
  - disable dump()
  - dump specific state based on arguments
  - run custom commands based on arguments

This CL also implements this method in the emulated vehicle HAL, where it adds
options to dump the user-related state.

Bug: 146207078

Test: adb shell lshal debug android.hardware.automotive.vehicle@2.0::IVehicle/default --user-hal
Test: atest android.hardware.automotive.vehicle@2.0-manager-unit-tests \
          android.hardware.automotive.vehicle@2.0-default-impl-unit-tests

Change-Id: If04e8222a31448f170ab2b54552051196b6ab958