feature #14403 [Form] deprecate read_only option (Tobion)

This PR was squashed before being merged into the 2.8 branch (closes #14403).

Discussion
----------

[Form] deprecate read_only option

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #10658
| License       | MIT
| Doc PR        | symfony/symfony-docs#3782

Replaces #10676 with a slightly different implementation.
- fixes BC break when 'read_only' => true option and at the same time custom attributes are used by using a normalizer
- adds deprecation notice
- keeps legacy tests

Commits
-------

53330e1 [Form] deprecate read_only option

Author: fabpot

Resources/views/Form/widget_attributes.html.php

@@ -1,12 +1,11 @@
-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 ?>
+id="<?php echo $view->escape($id) ?>" name="<?php echo $view->escape($full_name) ?>"<?php if ($disabled): ?> disabled="disabled"<?php endif ?>
+<?php if ($required): ?> required="required"<?php endif ?>
 <?php foreach ($attr as $k => $v): ?>
 <?php if (in_array($k, array('placeholder', 'title'), true)): ?>
-<?php printf('%s="%s" ', $view->escape($k), $view->escape($view['translator']->trans($v, array(), $translation_domain))) ?>
+<?php printf(' %s="%s"', $view->escape($k), $view->escape($view['translator']->trans($v, array(), $translation_domain))) ?>
 <?php elseif ($v === true): ?>
-<?php printf('%s="%s" ', $view->escape($k), $view->escape($k)) ?>
+<?php printf(' %s="%s"', $view->escape($k), $view->escape($k)) ?>
 <?php elseif ($v !== false): ?>
-<?php printf('%s="%s" ', $view->escape($k), $view->escape($v)) ?>
+<?php printf(' %s="%s"', $view->escape($k), $view->escape($v)) ?>
 <?php endif ?>
 <?php endforeach ?>

composer.json

@@ -41,7 +41,7 @@
         "symfony/finder": "~2.0,>=2.0.5|~3.0.0",
         "symfony/intl": "~2.3|~3.0.0",
         "symfony/security": "~2.6|~3.0.0",
-        "symfony/form": "~2.7|~3.0.0",
+        "symfony/form": "~2.8|~3.0.0",
         "symfony/class-loader": "~2.1|~3.0.0",
         "symfony/expression-language": "~2.6|~3.0.0",
         "symfony/process": "~2.0,>=2.0.5|~3.0.0",