Accept methods returning Task

[jnyrup]

Validation.Integration.WCF naturally does not support async methods decorated with [OperationContract].

This blog post describes the path to add support for async Begin/End pattern.
https://philippetruche.wordpress.com/2008/07/14/using-the-enterprise-library-validation-block-with-wcf-asynchronous-operations/

Adding support async methods returning Task or Task<T> is similar.
In addition to checking on operation.SyncMethod it should also check operation.TaskMethod.

I've been using that check for ~2 years now with net472 projects, but we want to migrate to .netstandard projects and possibly avoid maintaining my own fork of Validation.Integration.WCF.

E.g.

ValidationBehavior.HasValidationAssertions(OperationDescription operation)
{
    MethodInfo methodInfo = operation.SyncMethod ?? operation.Task;
    ...
}

public ValidationParameterInspector(OperationDescription operation, string ruleSet)
{
    MethodInfo method = operation.SyncMethod ?? operation.Task;
    ...
}