Attribute certificate printing functions

Attribute certificate printing functions

Add functions to print an attribute certificate.  Several
attribute value types defined by the RFC 5755 specification
are multi-field values (i.e ASN1_SEQUENCE rather than an ASN1_STRING
or similar format).  Currently those values are printed using
`ASN1_item_print`.  A more user-friendly output mechanism (maybe
similar to the i2r_ functions used for X509 extensions) could be
added in future.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15857)