minor #9488 csrf_token now can be used without installing the Form component (javiereguiluz)

This PR was squashed before being merged into the master branch (closes #9488).

Discussion
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csrf_token now can be used without installing the Form component

This fixes #9488.

@xabbuh in your original code (https://github.com/symfony/symfony/pull/25197/files) the function was added to Twig Bridge so ... could you please verify if installing just `security-csrf` is enough to use this function or if we need to install some other package? Thanks!

Commits
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3c48a0a csrf_token now can be used without installing the Form component

Author: javiereguiluz

security/csrf.rst

@@ -12,12 +12,11 @@ CSRF protection works by adding a hidden field to your form that contains a
 value that only you and your user know. This ensures that the user - not some
 other entity - is submitting the given data.
 
-Before using the CSRF protection, install it in your project (which in turn
-requires installing the Symfony Form component):
+Before using the CSRF protection, install it in your project:
 
 .. code-block:: terminal
 
-    $ composer require security-csrf form
+    $ composer require security-csrf
 
 Then, enable/disable the CSRF protection with the ``csrf_protection`` option
 (see the :ref:`CSRF configuration reference <reference-framework-csrf-protection>`
@@ -278,6 +277,10 @@ After this, you have protected your login form against CSRF attacks.
 CSRF Protection in HTML Forms
 -----------------------------
 
+.. versionadded:: 4.1
+    In Symfony versions prior to 4.1, CSRF support required installing the
+    Symfony Form component even if you didn't use it.
+
 It's also possible to add CSRF protection to regular HTML forms not managed by
 the Symfony Form component, for example the simple forms used to delete items.
 First, use the ``csrf_token()`` function in the Twig template to generate a CSRF