forms: add class when rendering a widget readonly (#18745)

wcs/qommon/templates/qommon/forms/widget.html

@@ -1,5 +1,6 @@
 {% load qommon %}
 <div class="widget {{widget.class_name}} {{widget.extra_css_class}}
+     {% if widget.readonly %}widget-readonly{% endif %}
      {% if widget.get_error %}widget-with-error{% endif %}
      {% if widget.get_message %}widget-with-message{% endif %}
      {% if widget.is_required %}widget-required{% else %}widget-optional{% endif %}