title: Npgsql support for getting jsonb field as stream
body: <p>I am trying to do the following on a jsonb field: </p>
  
  <pre><code>using (var reader = cmd.ExecuteReader())
  {
      while (reader.Read())
      {
          using (var results = reader.GetStream(0))
          {
              results.CopyTo(stream);
          }
      }
      reader.Close();
  }
  </code></pre>
  
  <p>and getting an exception telling me that GetStream is not supported for this field.
  Am I missing something here or is it Npgsql that simply doesn't support streaming jsonb fields (yet)?</p>