EVP & TLS: Add necessary EC_KEY data extraction functions, and use them

EVP & TLS: Add necessary EC_KEY data extraction functions, and use them

libssl code uses EVP_PKEY_get0_EC_KEY() to extract certain basic data
from the EC_KEY.  We replace that with internal EVP_PKEY functions.

This may or may not be refactored later on.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11358)