Prepare to provide EVP_Digest{Sign,Verify}

Prepare to provide EVP_Digest{Sign,Verify}

These are one-shot versions combining EVP_Digest{Sign,Verify}{Update,Final}.
and are part of the OpenSSL 1.1.1 API. While they simplify callers in some
situations slightly, their real use is for EdDSA that by design can't be
split into Update/Final steps.

Based on OpenSSL commit 7539418981c140648a620d72edd7398564878b5c

ok inoguchi