Prepare to provide EVP_PKEY_check()

Prepare to provide EVP_PKEY_check()

This allows checking the validity of an EVP_PKEY. Only RSA and EC keys
are supported. If a check function is set the EVP_PKEY_METHOD, it will
be used, otherwise the check function on the EVP_PKEY_ASN1_METHOD is
used.  The default ASN.1 methods wrap RSA_check_key() and
EC_KEY_check_key(), respectively.

The corresponding setters are EVP_PKEY_{asn1,meth}_set_check().

It is unclear why the PKEY method has no const while the ASN.1 method
has const.

Requested by tobhe and used by PHP 8.1.
Based on OpenSSL commit 2aee35d3

ok inoguchi jsing