EVP: Preserve the EVP_PKEY id in a few more spots

EVP: Preserve the EVP_PKEY id in a few more spots

As long as there are internal legacy keys for EVP_PKEY, we need to preserve
the EVP_PKEY numeric identity when generating a key, and when creating the
EVP_PKEY_CTX.

For added consistency, the EVP_PKEY_CTX contructor tries a little
harder to find a EVP_PKEY_METHOD.  Otherwise, we may run into
situations where the EVP_PKEY_CTX ends up having no associated methods
at all.

Reviewed-by: Paul Yang <kaishen.yy@antfin.com>
(Merged from https://github.com/openssl/openssl/pull/12785)