use label instead of placeholder for fieldset legend

Author: mjauvin

modules/backend/formwidgets/FieldSet.php

@@ -23,6 +23,8 @@ class FieldSet extends FormWidgetBase
      */
     public $form;
 
+    public $showLabels = false;
+
     /**
      * @var Form form widget reference
      */

modules/backend/formwidgets/fieldset/partials/_fieldset.php

@@ -1,8 +1,8 @@
-<?php $placeholder = object_get($this->config, 'placeholder'); ?>
+<?php $label = object_get($this->config, 'label'); ?>
 
 <fieldset class="fieldset">
-    <?php if ($placeholder): ?>
-        <legend><?= trans($placeholder) ?></legend>
+    <?php if ($label): ?>
+        <legend><?= trans($label) ?></legend>
     <?php endif ?>
 
     <?= $this->formWidget->render() ?>