[Form] Fix BC break introduced in #14403

Author: HeahDude

Resources/views/Form/widget_attributes.html.php

@@ -1,6 +1,8 @@
-id="<?php echo $view->escape($id) ?>" name="<?php echo $view->escape($full_name) ?>"<?php if ($disabled): ?> disabled="disabled"<?php endif ?>
+id="<?php echo $view->escape($id) ?>" name="<?php echo $view->escape($full_name) ?>"<?php if ($read_only): ?> readonly="readonly"<?php endif ?>
+<?php if ($disabled): ?> disabled="disabled"<?php endif ?>
 <?php if ($required): ?> required="required"<?php endif ?>
 <?php foreach ($attr as $k => $v): ?>
+<?php if ('readonly' === $k) { continue; } ?>
 <?php if (in_array($k, array('placeholder', 'title'), true)): ?>
 <?php printf(' %s="%s"', $view->escape($k), $view->escape(false !== $translation_domain ? $view['translator']->trans($v, array(), $translation_domain) : $v)) ?>
 <?php elseif ($v === true): ?>

composer.json

@@ -43,7 +43,7 @@
         "symfony/dom-crawler": "~2.0,>=2.0.5|~3.0.0",
         "symfony/polyfill-intl-icu": "~1.0",
         "symfony/security": "~2.6|~3.0.0",
-        "symfony/form": "~2.8",
+        "symfony/form": "^2.8.4",
         "symfony/expression-language": "~2.6|~3.0.0",
         "symfony/process": "~2.0,>=2.0.5|~3.0.0",
         "symfony/validator": "~2.5|~3.0.0",