Add a unit test for remote_prov_utils

This functionality will be used for the factory tooling, so we should
test it. Additionally, some new functionality will soon be added, and
it also needs to be tested.

Ignore-AOSP-First: No merge path to aosp, will manually merge
Test: libkeymint_remote_prov_support_test
Bug: 191301285
Change-Id: I6a8798fc4b09fff1e829185a4b9e471921e5d2a9