@CanIgnoreReturnValue
    public Builder setVariant(Variant variant) {
      this.variant = variant;
      return this;
    }
Current implementation only accepts certain NO_PREFIX instances of AesGcmParameters,
AesCtrHmacAeadParameters, XChaCha20Poly1305Parameters or AesSivParameters.
java_src/src/main/java/com/google/crypto/tink/hybrid/EciesParameters.java