…dler_id is not provided (Youssef BENHSSAIEN)

This PR was squashed before being merged into the 3.4 branch.

Discussion
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[FrameworkBundle] set default session.handler alias if handler_id is not provided

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #37245
| License       | MIT
| Doc PR        |

Without a configured [`handler_id`](https://symfony.com/doc/current/session.html#configuration), the `session.handler` alias is not created, and somes services depend on this alias specialy.

Related to the reported issue above (affected version 4.4.9), the `ServiceHandlerInterface` is an alias of `session.handler`, when execute :
- `bin/console debug:container session.handler` : The alias is not defined, so the `ContainerDebugCommand` look for a service containing the `session.handler` as part of his name (ContainerDebugCommand::findServiceIdsContaining() is called and returns by default `session.handler.native_file`)
-  `bin/console debug:container SessionHandlerInterface` : The service is defined as an alias of `session.handler`, when calling `ContainerBuilder::getDefinition('session.handler')` the exception occured as the alias is not defined.

# Implemented solution
Create a default `session.handler` when the param `handler_id` is not provided (I choosed `session.handler.native_file` rather than `NullSessionHandler`).

# Affected versions
From [`3.4`](https://github.com/symfony/framework-bundle/blob/3.4/DependencyInjection/FrameworkExtension.php#L879) to [`5.1`](https://github.com/symfony/framework-bundle/blob/5.1/DependencyInjection/FrameworkExtension.php#L955)

Commits
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46c8c37 [FrameworkBundle] set default session.handler alias if handler_id is not provided