EntityPrintController::viewPrint should not send the response.

Problem/Motivation

In the EntityPrintController, the viewPrint method is sending the response rather than returning the response object.

  public function viewPrint($export_type, $entity_type, $entity_id) {
    // Create the Print engine plugin.
    $config = $this->config('entity_print.settings');
    $entity = $this->entityTypeManager->getStorage($entity_type)->load($entity_id);

    $print_engine = $this->pluginManager->createSelectedInstance($export_type);
    return (new StreamedResponse(function () use ($entity, $print_engine, $config) {
      // The Print is sent straight to the browser.
      $this->printBuilder->deliverPrintable([$entity], $print_engine, $config->get('force_download'), $config->get('default_css'));
    }))->send();
  }

In a decoupled setting, if you try to fetch the route to be able to get the PDF, you get the following error in the Drupal site:

RuntimeException: Failed to start the session because headers have already been sent by "/var/www/html/vendor/dompdf/dompdf/src/Adapter/CPDF.php"

Steps to reproduce

Example JS:

 const response = await fetch(`https://example.com/print/pdf/commerce_order/${order.drupal_internal__order_id}`, {
      headers: {
        'Authorization': `Bearer ${token.access_token}`,
      },
    });
    if (response.ok) {
      const blob = await response.blob();
      const file = window.URL.createObjectURL(blob);
      window.location.assign(file);
    }

Proposed resolution

Return the response object and let Drupal handle sending it.