When getting the session's id, check if the session is not closed

This introduced a regression from #9246, with an incomplete fix ;
As the `started` flag on the NativeSessionStorage was not `true`
anymore when saving the session, the session id was always empty
when saving it, and thus when sending the `PHPSESSID` cookie
bug #9625 [HttpFoundation] Do not return an empty session id if the session was closed (Taluu)

This PR was merged into the 2.2 branch.

Discussion
----------

[HttpFoundation] Do not return an empty session id if the session was closed

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7936
| License       | MIT
| Doc PR        | ~

A regression from the bug fix #9246 was introduced due to an incomplete fix ;

As the `started` flag on the NativeSessionStorage was not `true` anymore when saving the session, the session id was always empty when saving it, and thus when sending the `PHPSESSID` cookie.

The previous PR I made (#9530) was another approach to solve this regression, but this one should keep the fix made by @tecbot on #9246, and finish it with another verification. I may miss another place where `started` is used, but I don't really see which other conditions depending on this property should be altered...

**Note : this is #9611 rebased on 2.2**

This should be mergeable.

Commits
-------

5b9a727 When getting the session's id, check if the session is not closed
Fixed the registration of validation.xml file when the form is disabled
bug #9443 [FrameworkBundle] Fixed the registration of validation.xml file when the form is disabled (hason)

This PR was submitted for the 2.1 branch but it was merged into the 2.2 branch instead (closes #9443).

Discussion
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[FrameworkBundle] Fixed the registration of validation.xml file when the form is disabled

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

Commits
-------

cfa5aa5 [FrameworkBundle] Fixed the registration of validation.xml file when the form is disabled
Fix DateType for 32bits computers.
bug #9314 [Form] Fix DateType for 32bits computers. (WedgeSama)

This PR was squashed before being merged into the 2.2 branch (closes #9314).

Discussion
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[Form] Fix DateType for 32bits computers.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #5227,#5554
| License       | MIT
| Doc PR        | -

Fix an issue due to 32bits machines, date can be only between 1902-2037.
Simply not add date if false. Can be good to add this to 2.3 and master too.

Commits
-------

b80fb43 [Form] Fix DateType for 32bits computers.
Modified guessDefaultEscapingStrategy to not escape txt templates

Useful for plaintext emails.
bug #9639 Modified guessDefaultEscapingStrategy to not escape txt templates (fabpot)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #9639).

Discussion
----------

Modified guessDefaultEscapingStrategy to not escape txt templates

This PR was submitted on the symfony/TwigBundle read-only repository and moved automatically to the main Symfony repository (closes symfony/TwigBundle#2).

Useful for plaintext emails.

Commits
-------

6affe94 Modified guessDefaultEscapingStrategy to not escape txt templates
Teardown used wrong property
minor #9640 Fixed wrong property in test teardown (fabpot)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #9640).

Discussion
----------

Fixed wrong property in test teardown

This PR was submitted on the symfony/EventDispatcher read-only repository and moved automatically to the main Symfony repository (closes symfony/EventDispatcher#2).

Commits
-------

5330603 Teardown used wrong property
Merge branch '2.2' into 2.3

* 2.2:
  Teardown used wrong property
  Modified guessDefaultEscapingStrategy to not escape txt templates
  Fix DateType for 32bits computers.
  Fixed the registration of validation.xml file when the form is disabled
  When getting the session's id, check if the session is not closed