[VarDumper] fix control chars styling
[EventDispatcher] perf optim
[HttpKernel] fix DebugHandlersListener
updated CHANGELOG for 2.3.21
update CONTRIBUTORS for 2.3.21
updated VERSION for 2.3.21
bumped Symfony version to 2.3.22
updated CHANGELOG for 2.5.6
updated VERSION for 2.5.6
bumped Symfony version to 2.5.7
Ensure that Twig form themes are always a list, not a hashmap

array_unique does not reindex arrays when deleting keys.
bug #12308 Ensure that Twig form themes are always a list, not a hashmap (stof)

This PR was merged into the 2.6-dev branch.

Discussion
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Ensure that Twig form themes are always a list, not a hashmap

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12305
| License       | MIT
| Doc PR        | n/a

array_unique does not reindex arrays when deleting keys.

Commits
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2a19cd8 Ensure that Twig form themes are always a list, not a hashmap
Improved the phpdoc for security token classes
[Security][listener] change priority of switchuser
[OptionsResolver] fix counting of options

and make sure the tests are compatible with phpunit strict mode
[OptionsResolver] fix invalid value exception formatting
[OptionsResolver] fix calling resolve from within closure
[OptionsResolver] add missing exception based on OutOfBoundsException and clarify message
minor #12310 Improved the phpdoc for security token classes (stof)

This PR was merged into the 2.3 branch.

Discussion
----------

Improved the phpdoc for security token classes

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

This will avoid to have Scrutinizer complaining that we pass an array of string rather than an array of RoleInterface for instance.

Commits
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7b6d115 Improved the phpdoc for security token classes
bug #12313 [Security][listener] change priority of switchuser (aitboudad)

This PR was merged into the 2.3 branch.

Discussion
----------

[Security][listener] change priority of switchuser

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Hi,
I have the following users:
  - Manager: Allowed to access to (/admin) and has a role ROLE_ALLOWED_TO_SWITCH
  - Partner: Allowed to access to (/partner)

When I attempt to switch to partner user I get "Access denied", well I think the switchuser listener must be registred before access listener.

Commits
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5f8047d [Security][listener] change priority of switchuser