X25519/X448 testing

[jvdsn]

What type of change is being proposed? Implement testing for X25519/X448 (aka ECDH with Curve25519 and Curve448).

Details on suggestion I am aware that X25519 and X448 are currently not yet FIPS-approved, as they are not specified in SP 800-56Ar3. However, it is my understanding that this omission is due to a lack of manpower in the NIST CT group, rather than any security concerns. Moreover, ACVP is not only used by FIPS validations, but also other standards-based evaluations (like Common Criteria under NIAP). It would be very useful to have X25519/X448 testing available for these evaluations, even if FIPS does not yet allow them. X25519 and X448 are also part of the TLS 1.3 specification, and therefore widely implemented in cryptographic libraries.