CMS sign digest

CMS sign digest

CLI changes: New parameter -digest to CLI command openssl cms, to
provide pre-computed digest for use with -sign.

API changes: New function CMS_final_digest(), like CMS_final() but
uses a pre-computed digest instead of computing it from the data.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/15348)