Use Drupal states library in Entity: load action.

Closes #3318507

modules/content/src/Service/EntityLoader.php

@@ -145,6 +145,14 @@ class EntityLoader {
       '#description' => $this->t('The type of the entity to be loaded.'),
       '#weight' => -60,
       '#eca_token_select_option' => TRUE,
+      '#states' => [
+        'invisible' => [
+          ':input[name="from"]' => ['value' => 'current'],
+        ],
+        'optional' => [
+          ':input[name="from"]' => ['value' => 'current'],
+        ],
+      ],
     ];
     $form['entity_id'] = [
       '#type' => 'textfield',
@@ -152,6 +160,14 @@ class EntityLoader {
       '#default_value' => $plugin_configuration['entity_id'],
       '#description' => $this->t('The ID of the entity to be loaded.'),
       '#weight' => -50,
+      '#states' => [
+        'visible' => [
+          ':input[name="from"]' => [['value' => 'id'], ['value' => '_eca_token']],
+        ],
+        'required' => [
+          ':input[name="from"]' => ['value' => 'id'],
+        ],
+      ],
     ];
     $form['revision_id'] = [
       '#type' => 'textfield',
@@ -166,6 +182,14 @@ class EntityLoader {
       '#default_value' => $plugin_configuration['properties'],
       '#description' => $this->t('A key-value list of raw field values of the entity to load. This will only be used when loading by properties is selected above. Supports YAML format. Example:<em><br/>field_mynumber: 1</em>. When using tokens and YAML altogether, make sure that tokens are wrapped as a string. Example: <em>title: "[node:title]"</em>'),
       '#eca_token_replacement' => TRUE,
+      '#states' => [
+        'visible' => [
+          ':input[name="from"]' => [['value' => 'properties'], ['value' => '_eca_token']],
+        ],
+        'required' => [
+          ':input[name="from"]' => ['value' => 'properties'],
+        ],
+      ],
     ];
     $form['langcode'] = [
       '#type' => 'select',