[3.8] bpo-38270: More fixes for strict crypto policy (GH-16418) (#16437)

[3.8] bpo-38270: More fixes for strict crypto policy (GH-16418) (#16437)

test_hmac and test_hashlib test built-in hashing implementations and
OpenSSL-based hashing implementations. Add more checks to skip OpenSSL
implementations when a strict crypto policy is active.

Use EVP_DigestInit_ex() instead of EVP_DigestInit() to initialize the
EVP context. The EVP_DigestInit() function clears alls flags and breaks
usedforsecurity flag again.

Signed-off-by: Christian Heimes <christian@python.org>
https://bugs.python.org/issue38270.
(cherry picked from commit 90558158093c0ad893102158fd3c2dd9f864e82e)

Co-authored-by: Christian Heimes <christian@python.org>