Extra stack generated by ClassCastException for target type check

Hi, Thanks for the great library.

Our flame graph shows there are extra stacks from creating ClassCastException.

By looking code, there are many of try-catch of ClassCastException to check whether the instance is a target type or not.

Since creation of ClassCastException creates extra stacks, it is better to check by !=null && instanceof.

For example, in SimpleJwkFilter:

String getCrv(JsonWebKey jwk)
{
    try
    {
        return ((EllipticCurveJsonWebKey) jwk).getCurveName();
    }
    catch (ClassCastException e)
    {
        return null;
    }
}

This can be written:

String getCrv(JsonWebKey jwk)
{
    // in this case, jwk is guaranteed to be not null, skipping null check
    if(!(jwk instanceof EllipticCurveJsonWebKey)) {
      return null;
    }
    return ((EllipticCurveJsonWebKey) jwk).getCurveName();
}

It is a tiny portion compare to entire application stack, but it is appreciated if you could remove try-catch, so that extra stack generation can be avoided.

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