Modal/dialog/ajax is using query parameters instead of accept headers

Modals are now using query parameters instead of accept headers, so for example test code to request a specific
page as modal would have the change like the following:

Before

$ajax_result = $this->drupalGetAjax('ajax-test/dialog-contents', array(), array('Accept: application/vnd.drupal-modal'));

After

$ajax_result = $this->drupalGetAjax('ajax-test/dialog-contents', array('query' => array(MainContentViewSubscriber::WRAPPER_FORMAT => 'drupal_modal')));

In case you generate some ajax settings its looking a bit different:

Before

  '#ajax' => [
    'callback' => '::preview',
    'event' => 'click',
    'url' => Url::fromRoute('system.ajax')->toString(),
    'dialogType' => 'modal',
    'accepts' => 'application/vnd.drupal-ajax',
  ]

After

  '#ajax' => [
    'callback' => '::preview',
    'event' => 'click',
    'url' => Url::fromRoute('system.ajax')->toString(),
    'dialogType' => 'modal',
  ]

If adding a modal in a render array, the change is similar to the above example, just not camelCased:

Before

  'attributes' => [
    'class' => ['use-ajax'],
    'data-accepts' => 'application/vnd.drupal-modal',
    'data-dialog-options' => Json::encode([
      'width' => 700,
    ]),
  ],

After

  'attributes' => [
    'class' => ['use-ajax'],
    'data-dialog-type' => 'modal',
    'data-dialog-options' => Json::encode([
      'width' => 700,
    ]),
  ],

A complete example of a link opening in a dialog:

    return [
      '#type' => 'link',
      '#title' => $this->t('Some text'),
      '#url' => Url::fromRoute('some.route', [], ['query' => $this->getDestinationArray()]),
      '#options' => ['attributes' => [
        'class' => ['use-ajax'],
        'data-dialog-type' => 'modal',
        'data-dialog-options' => Json::encode([
          'width' => 700,
        ]),
      ]],
      '#attached' => ['library' => ['core/drupal.dialog.ajax']],
    ];

Most importantly, don't forget to attach the dialog library.