feature #16755 [Security] add subject variable to expression context (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
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[Security] add subject variable to expression context

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #16600
| License       | MIT
| Doc PR        | TODO

Commits
-------

346943e add subject variable to expression context

UPGRADE-2.8.md

@@ -448,6 +448,9 @@ FrameworkBundle
 Security
 --------
 
+ * The `object` variable passed to expressions evaluated by the `ExpressionVoter`
+   is deprecated. Instead use the new `subject` variable.
+
  * The `AbstractVoter` class was deprecated. Instead, extend the `Voter` class and
    move your voting logic in the `supports($attribute, $subject)` and
    `voteOnAttribute($attribute, $object, TokenInterface $token)` methods.

src/Symfony/Component/Security/Core/Authorization/Voter/ExpressionVoter.php

@@ -102,6 +102,7 @@ class ExpressionVoter implements VoterInterface
             'token' => $token,
             'user' => $token->getUser(),
             'object' => $object,
+            'subject' => $object,
             'roles' => array_map(function ($role) { return $role->getRole(); }, $roles),
             'trust_resolver' => $this->trustResolver,
         );