Update file JsonText.php

Closes #3450162

src/Element/JsonText.php

@@ -3,12 +3,17 @@
 namespace Drupal\json_field\Element;
 
 use Drupal\Component\Render\FormattableMarkup;
+// Deprecated class.
 use Drupal\Core\Render\Element\RenderElement;
 use Drupal\json_field\JsonMarkup;
 
 /**
  * Provides a JSON text render element.
  *
+ * @deprecated in drupal:10.3.0 and is removed from drupal:12.0.0.
+ *   Use \Drupal\Core\Render\Element\RenderElementBase instead.
+ *   @see https://www.drupal.org/node/3436275
+ *
  * @RenderElement("json_text")
  */
 class JsonText extends RenderElement {