title: serializeasync object to utf8jsonwriter with System.Text.Json
body: <p>In dotnet3.1, using System.Text.Json</p>
  <p>How to asynchronous serialize a c# object to a utf8jsonwriter ?
  I find the Serialize() method but not the Async version and I'm writing to a stream so I'm having error:
  &quot;Error while copying to stream... Synchronous operations are disallowed....&quot; if I use sync Serialize()</p>
  <p>my code is very simple:</p>
  <pre><code>Stream responseStream;
  var jsonWriter = new Utf8JsonWriter(responseStream);
  await JsonSerializer.SerializeAsync(jsonWriter, obj);
  </code></pre>
  <p>where obj is an class instance DTO.</p>
  <p>I see there is an overload receiving a Stream but I need to write using the Utf8JsonWriter jsonWriter which wraps the target stream.</p>