Implement signature functions for EVP_PKEY MAC to EVP_MAC provider bridge

Implement signature functions for EVP_PKEY MAC to EVP_MAC provider bridge

Some MAC implementations were available before the current EVP_MAC API. They
were used via EVP_DigestSign*. There exists a bridge between the oldAPI and
the EVP_MAC API however this bridge itself uses a legacy EVP_PKEY_METHOD.
This commit implements the signature functions for the provider side bridge
without having to use any legacy code.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/12637)