Issue #3088681 by phenaproxima, seanB, bnjmnm, lauriii: Make MediaLibraryTest less dependent on representational CSS selectors

(cherry picked from commit 1aaa1d95e0)

core/modules/media_library/js/media_library.widget.es6.js

@@ -58,7 +58,7 @@
                 ? strings.hide
                 : strings.show,
             )
-            .parent()
+            .closest('.js-media-library-widget')
             .find('.js-media-library-item-weight')
             .parent()
             .toggle();

core/modules/media_library/js/media_library.widget.js

@@ -31,7 +31,7 @@
       };
       $('.js-media-library-widget-toggle-weight', context).once('media-library-toggle').on('click', function (e) {
         e.preventDefault();
-        $(e.currentTarget).toggleClass('active').text($(e.currentTarget).hasClass('active') ? strings.hide : strings.show).parent().find('.js-media-library-item-weight').parent().toggle();
+        $(e.currentTarget).toggleClass('active').text($(e.currentTarget).hasClass('active') ? strings.hide : strings.show).closest('.js-media-library-widget').find('.js-media-library-item-weight').parent().toggle();
       }).text(strings.show);
       $('.js-media-library-item-weight', context).once('media-library-toggle').parent().hide();
     }

core/modules/media_library/src/Form/AddFormBase.php

@@ -173,6 +173,7 @@ abstract class AddFormBase extends FormBase {
         '#type' => 'container',
         '#attributes' => [
           'class' => [
+            'js-media-library-add-form-added-media',
             'media-library-add-form__added-media',
           ],
           'aria-label' => $this->t('Added media items'),

core/modules/media_library/src/Plugin/Field/FieldWidget/MediaLibraryWidget.php

@@ -317,7 +317,7 @@ class MediaLibraryWidget extends WidgetBase implements ContainerFactoryPluginInt
       '#target_bundles' => isset($settings['target_bundles']) ? $settings['target_bundles'] : FALSE,
       '#attributes' => [
         'id' => $wrapper_id,
-        'class' => ['media-library-widget'],
+        'class' => ['js-media-library-widget', 'media-library-widget'],
       ],
       '#attached' => [
         'library' => ['media_library/widget'],