Add Ed25519 algorithm.

Reinstate Ed25519 algorithm to curv25519.c this is largely just a copy of
the code from BoringSSL with some adjustments so it compiles under OpenSSL.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3503)

crypto/ec/ec_lcl.h

@@ -608,6 +608,15 @@ int ossl_ecdsa_verify(int type, const unsigned char *dgst, int dgst_len,
 int ossl_ecdsa_verify_sig(const unsigned char *dgst, int dgst_len,
                           const ECDSA_SIG *sig, EC_KEY *eckey);
 
+void ED25519_keypair(uint8_t out_public_key[32], uint8_t out_private_key[64]);
+int ED25519_sign(uint8_t *out_sig, const uint8_t *message, size_t message_len,
+                 const uint8_t private_key[64]);
+int ED25519_verify(const uint8_t *message, size_t message_len,
+                   const uint8_t signature[64], const uint8_t public_key[32]);
+void ED25519_keypair_from_seed(uint8_t out_public_key[32],
+                               uint8_t out_private_key[64],
+                               const uint8_t seed[32]);
+
 int X25519(uint8_t out_shared_key[32], const uint8_t private_key[32],
            const uint8_t peer_public_value[32]);
 void X25519_public_from_private(uint8_t out_public_value[32],