[HttpKernel][2.6] Adding support for invokable controllers in the RequestDataCollector
bug #12443 [HttpKernel][2.6] Adding support for invokable controllers in the RequestDataCollector (jameshalsall)

This PR was submitted for the master branch but it was merged into the 2.5 branch instead (closes #12443).

Discussion
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[HttpKernel][2.6] Adding support for invokable controllers in the RequestDataCollector

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

As part of https://github.com/symfony/symfony/pull/11193 support for controllers using `__invoke()` was added.

The `RequestDataCollector` did not support controllers that were defined in the routing as...

```php
route_name:
    path: /{id}
    defaults: { _controller: acme_app.page.controller.page }
    requirements:
        id: \d+
```

Where the controller was defined as...

```php
class PageController
{
    public function __invoke()
    {
        //
    }
}
```

This PR adds that support. Tests have been updated.

Commits
-------

f1d043a [HttpKernel][2.6] Adding support for invokable controllers in the RequestDataCollector