Ensure the EVP_PKEY operation_cache is appropriately locked

Ensure the EVP_PKEY operation_cache is appropriately locked

The EVP_PKEY operation_cache caches references to provider side key
objects that have previously been exported for this EVP_PKEY, and their
associated key managers. The cache may be updated from time to time as the
EVP_PKEY is exported to more providers. Since an EVP_PKEY may be shared by
multiple threads simultaneously we must be careful to ensure the cache
updates are locked.

Fixes #13818

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13987)