VmsUtils: Add new methods to parse availability state messages

These methods are needed in the HAL client to parse sequence number and
associated layers when the availablity of the VMS layers change.
HAL client relies on these messages by either explicitly requesting the
availability or through availability change message sent by the Car
service.

Bug: 144434783
Fixes: 144434783

Test: Added new tests for the new methods. Ran the tests on Hawk.
Change-Id: I09497640367a894e1dfb6143ac3bbdb63d64b53e