Transitioning identity to external_libcppbor

This change removes hardware/interfaces/identity's dependency on its own
libcppbor copy. The copy can not be fully removed until various vendor
dependencies are cleaned up.

Superficial changes are made to the VTS tests to match the slightly
altered namespace on some of the functions.

This migration is a prerequisite for getting the
IRemotelyProvisionedComponent functionality into system/keymaster.
Without migrating to the same library, the build system runs into issues
since there are "two" libcppbor libraries with conflicting namespaces
otherwise.

Bug: 182445123
Test: atest VtsHalIdentityTargetTest
Change-Id: I854ffa31c4adb5a3d1df06539fe66075ccc4625d