title: IAsyncEnumerable not working with in Visual Studio project that targets .Net 4.8
body: <p>When attempting to use <code>IAsyncEnumerable</code>, I get this error:</p>
  
  <blockquote>
    <p>The type or namespace name IAsyncEnumerable&lt;> could not be found (are you missing a using directive or assembly reference?)</p>
  </blockquote>
  
  <p>How do I make this compatible with c# 8?</p>