Make EVP_MD_CTX_ctrl() work for legacy use cases (ssl3).

This is still required currently by engines and digestsign/digestverify.
This PR contains merged in code from Richard Levitte's PR #9126.

[extended tests]

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9103)