symfony

This PR was merged into the 3.4 branch.

Discussion
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[HttpKernel] Move services reset to Kernel::handle()+boot()

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #24552
| License       | MIT
| Doc PR        | -

This is an alternative to #24697 (which uses middlewares).
This PR adds a new `services_resetter` service that the Kernel calls on 2nd root requests to reset services.
Instead of #24697 which plans for optional enabling of the services reset, this approach moves the responsibility of calling the services resetter to the core Kernel class, so that no configuration/middleware/etc. is required at all, and no overhead exists at all for regular requests.

Commits
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4501a368 [HttpKernel] Move services reset to Kernel