Add OSSL_PARAM_dup() and OSSL_PARAM_merge().

Add OSSL_PARAM_dup() and OSSL_PARAM_merge().

These functions are prerequisites for implementing EVP_PKEY_todata().

OSSL_PARAM_dup() is required to make a deep copy of the exported
params (since the provider export() uses a OSSL_PARAM_BLD which throws away the
data after the call), and then use OSSL_PARAM_merge() to add some additional params
that can be passed to the EVP_PKEY_todata().

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14785)