public static ECPublicKey getEcPublicKey(final byte[] x509PublicKey)
      throws GeneralSecurityException {
    KeyFactory kf = EngineFactory.KEY_FACTORY.getInstance("EC");
    return (ECPublicKey) kf.generatePublic(new X509EncodedKeySpec(x509PublicKey));
  }
Returns an {@link ECPublicKey} from {@code x509PublicKey} which is an encoding of a public
key, encoded according to the ASN.1 type SubjectPublicKeyInfo.

TODO(b/68672497): test that in Java one can always get this representation by using
{@link ECPublicKey#getEncoded), regardless of the provider.
java_src/src/main/java/com/google/crypto/tink/subtle/EllipticCurves.java