Issue #2230955 by brantwynn: Move block.js to correct /js folder.

core/modules/block/block.libraries.yml

 drupal.block:
   version: VERSION
   js:
-    block.js: {}
+    js/block.js: {}
   dependencies:
     - core/jquery
     - core/drupal

core/modules/block/lib/Drupal/block/BlockFormController.php

@@ -111,7 +111,9 @@ public function form(array $form, array &$form_state) {
       '#type' => 'vertical_tabs',
       '#title' => $this->t('Visibility settings'),
       '#attached' => array(
-        'js' => array(drupal_get_path('module', 'block') . '/block.js'),
+        'library' => array(
+          'block/drupal.block',
+        ),
       ),
       '#tree' => TRUE,
       '#weight' => 10,