API for loading a provider

In previous versions, I was able to load an engine using `OpenSSL::Engine.load()` and `OpenSSL::Engine.by_id("pkcs11")`. Now that engine support has been removed, I've installed a matching OpenSSL 3.0 provider, but there seems to be no Ruby equivalent for `openssl pkey -provider pkcs11` (I believe that's `OSSL_PROVIDER_load()`).