Make a proper Python internal API for test PSA dependency inference #7845
Description
We have some Python code to automatically determine the dependencies of a test case using the PSA crypto API based on the mechanisms that it uses.
The basic idea is that any code that uses a PSA_xxx value has a dependency on PSA_WANT_xxx, but there are additional compliations: PSA_ECC_CURVE_xxx and PSA_DH_GROUP_xxx also encode the size in the PSA_WANT symbol; PSA_KEY_TYPE_xxx_KEY_PAIR also encode the operation in the PSA_WANT symbol.
The code to deal with these complications, as of 717a831 (mbedtls 3.4+), is mostly in generate_psa_tests.py, partly at the top and partly special cases in various functions (in particular, related to key pair usage, following the work around #7439). There's also some independent code in the bitrotting set_psa_test_dependencies.py (which we used to translate MBEDTLS_xxx dependencies to PSA dependencies a while ago, but don't use regularly now).
#7803 starts to move this code into a new Python module psa_information.py so that it can be used in code that's independent from the code in generate_psa_tests.py that's about enumerating all crypto mechanisms.
The goal of this task is to factor the recode in generate_psa_tests.py (or, by the time we address this issue, code that was originally in generate_psa_tests.py) so that callers can generally call one function/method infer_psa_dependencies which goes and analyzes the mechanisms that the test case uses and generates the PSA_WANT dependency list. That function would probably need an extra argument indicating what's done with the key involved (at least for the common case of having ≤1 key) to distinguish between the KEY_PAIR usage variants. Designing the exact interface (function names, argument lists, etc.) is part of this task. We just needs an interface that works now, not one that's fully future-proof, since the interface can evolve as needed.