minor #15527 [Form] Document using TranslatableMessage in form help (javiereguiluz)

This PR was squashed before being merged into the 5.4 branch.

Discussion
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[Form] Document using TranslatableMessage in form help

Fixes #15482.

Commits
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a6d4c40 [Form] Document using TranslatableMessage in form help

Author: javiereguiluz

reference/forms/types/options/help.rst.inc

@@ -1,11 +1,25 @@
 help
 ~~~~
 
-**type**: ``string`` **default**: null
+**type**: ``string`` or ``TranslatableMessage`` **default**: null
 
 Allows you to define a help message for the form field, which by default is
 rendered below the field::
 
-    $builder->add('zipCode', null, [
-        'help' => 'The ZIP/Postal code for your credit card\'s billing address.',
-    ]);
+    use Symfony\Component\Translation\TranslatableMessage;
+
+    $builder
+        ->add('zipCode', null, [
+            'help' => 'The ZIP/Postal code for your credit card\'s billing address.',
+        ])
+
+        // ...
+
+        ->add('status', null, [
+            'help' => new TranslatableMessage('order.status', ['%order_id%' => $order->getId()], 'store'),
+        ])
+    ;
+
+.. versionadded:: 5.4
+
+    Support for passing ``TranslatableMessage`` objects was introduced in Symfony 5.4.