No XDH or XEC AlgorithmParameters impl in JDK.

It order to get AlgorithmParameters from AlgorithmParameterSpec, applications could code as the general tyle for "EC" or other algorithms:
AlgorithmParameters algParams =
    AlgorithmParameters.getInstance("x25519");
algParams.init(x25519AlgorithmParamSpec);

If no implementation of XDH AlgorithmParameters, it is tricky to get AlgorithmParameters object for x25519/x448. Some public APIs requires to use AlgorithmParameters object, for example AlgorithmConstraints.permits().