class FormBuilderWrapper

class FormBuilderWrapper extends FormBuilder {
    
    /**
     * @var array
     */
    private $buildForms;
    
    /**
     * @return array
     */
    public function getBuildForm() {
        return $this->buildForms;
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareForm($form_id, &$form, FormStateInterface &$form_state) {
        parent::prepareForm($form_id, $form, $form_state);
        if (!$this->buildForms) {
            $this->buildForms = [];
        }
        $elements = [];
        foreach ($form as $key => $value) {
            if (strpos($key, '#') !== 0) {
                $elements[$key]['#title'] = isset($value['#title']) ? $value['#title'] : NULL;
                $elements[$key]['#access'] = isset($value['#access']) ? $value['#access'] : NULL;
                $elements[$key]['#type'] = isset($value['#type']) ? $value['#type'] : NULL;
            }
        }
        $buildInfo = $form_state->getBuildInfo();
        $class = get_class($buildInfo['callback_object']);
        $method = new \ReflectionMethod($class, 'buildForm');
        $this->buildForms[$buildInfo['form_id']] = [
            'class' => [
                'class' => $class,
                'method' => 'buildForm',
                'file' => $method->getFilename(),
                'line' => $method->getStartLine(),
            ],
            'form' => $elements,
        ];
        return $form;
    }

}