Support MBEDTLS_THREADING_ALT in the mutex usage verification framework

[gilles-peskine-arm]

The mutex usage verification framework should work with MBEDTLS_THREADING_ALT, because it's part of how a platform integrator can test that their threading abstraction matches our requirements.

This issue spans both the framework repository and the consuming repository(ies). At least in TF-PSA-Crypto, and ideally in 3.6 as well, have an all.sh component that runs with MBEDTLS_THREADING_ALT, with the mutex usage verification framework enabled.

Closely related: #206. I'm not sure if it makes more sense to do 206 before 207, 207 before 206, or both together.