ENCODER PROV: Add encoders with EncryptedPrivateKeyInfo output

ENCODER PROV: Add encoders with EncryptedPrivateKeyInfo output

Since EncryptedPrivateKeyInfo is a recognised structure, it's
reasonable to think that someone might want to specify it.

To be noted is that if someone specifies the structure PrivateKeyInfo
but has also passed a passphrase callback, the result will still
become a EncryptedPrivateKeyInfo structure.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16466)