Test X25519 key exchange

Test that X25519 key agreement works with Keystore-backed keys.

This is tested by generating two X25519 key pairs, using the private
key from each with the public key of the other for key agreement, and
comparing the secrets.

Bug: 194359292
Test: atest android.keystore.cts.Curve25519Test
Change-Id: I42ee0297fbca9b2bc430647070b44639b4179489
1 file changed