Add the missing security Twig functions to the dummy extension

[Amoifr]

While documenting the access_decision() Twig functions in symfony/symfony-docs#22452, the Code Blocks check failed with:

[Twig] Unknown "access_decision" function.
[Twig] Unknown "access_decision_for_user" function.

The functions do exist (they are registered by Symfony\Bridge\Twig\Extension\SecurityExtension), but they are missing from DummyExtension, so any new Twig code block using them is reported as invalid.

Comparing SecurityExtension::getFunctions() with DummyExtension, 5 of its 8 functions were missing:

• is_granted_for_user
• access_decision
• access_decision_for_user
• impersonation_path
• impersonation_url

Three of them (is_granted_for_user, impersonation_path, impersonation_url) are already documented in reference/twig_reference.rst; they go unnoticed today only because their code blocks predate the baseline.

The added test fails on main (1 issue reported) and passes with this change.

Thanks a lot for maintaining this tool — it caught a real mistake of mine in the very same PR, so I'm happy to give a little back. 🙂