Added form fieldset before html to \Magento\Framework\Data\Form\Element\Fieldset in getElementHtml() method

Author: Vasilii Burlacu

lib/internal/Magento/Framework/Data/Form/Element/Fieldset.php

@@ -43,7 +43,8 @@ public function __construct(
      */
     public function getElementHtml()
     {
-        $html = '<fieldset id="' . $this->getHtmlId() . '"' . $this->serialize(
+        $html = $this->getBeforeElementHtml();
+        $html .= '<fieldset area-hidden="false" id="' . $this->getHtmlId() . '"' . $this->serialize(
             ['class']
         ) . $this->_getUiId() . '>' . "\n";
         if ($this->getLegend()) {