Add missing sequence setup methods ReturnsAsync and ThrowsAsync for ValueTask<TResult>

[stakx]

The sequence setup API is incomplete: it is missing the ReturnsAsync and ThrowsAsync method overloads for ValueTask<TResult>:

public interface IHaveAsyncMethods
{
    Task<int> GetIntTask();
    ValueTask<int> GetIntValueTask();
}

var mock = new Mock<IHaveAsyncMethods>();

mock.Setup(m => m.GetIntTask()).ReturnsAsync(1);
mock.Setup(m => m.GetIntValueTask()).ReturnsAsync(2);
mock.SetupSequence(m => m.GetIntTask()).ReturnsAsync(3);
mock.SetupSequence(m => m.GetIntValueTask()).ReturnsAsync(4);  // missing method
mock.Setup(m => m.GetIntTask()).ThrowsAsync(new Exception("5"));
mock.Setup(m => m.GetIntValueTask()).ThrowsAsync(new Exception("6"));
mock.SetupSequence(m => m.GetIntTask()).ThrowsAsync(new Exception("7"));
mock.SetupSequence(m => m.GetIntValueTask()).ThrowsAsync(new Exception("8"));  // missing method

For completeness and consistency, these should be added.

(This perhaps shouldn't happen right now since we've decided to freeze Moq 4's API for the time being, while the initial release for Moq 5 is being finalized.)

/cc @kzu