DECODER: Allow precise result type for OSSL_DECODER_CTX_new_by_EVP_PKEY()

DECODER: Allow precise result type for OSSL_DECODER_CTX_new_by_EVP_PKEY()

There is some data that is very difficult to guess.  For example, DSA
parameters and X9.42 DH parameters look exactly the same, a SEQUENCE
of 3 INTEGER.  Therefore, callers may need the possibility to select
the exact keytype that they expect to get.

This will also allow use to translate d2i_TYPEPrivateKey(),
d2i_TYPEPublicKey() and d2i_TYPEParams() into OSSL_DECODER terms much
more smoothly.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13061)