Document new invokable factories (and configurators) implemented in symfony/symfony#30255.

Document new invokable factories (and configurators) implemented in symfony/symfony#30255.

…aldwin)

This PR was squashed before being merged into the 4.3-dev branch (closes #30255).

Discussion
----------

[DependencyInjection] Invokable Factory Services

| Q             | A
| ------------- | ---
| Branch?       | `master`
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        | symfony/symfony-docs#11014

> Failing test is in the Twig bridge, and outside of the the scope of this PR.

Allow referencing invokable factory services, just as route definitions reference invokable controllers.
This functionality was also added for service configurators for consistency.

## Example

```php
<?php

namespace App\Factory;

class ServiceFactory
{
    public function __invoke(bool $debug)
    {
        return new Service($debug);
    }
}
```

```yaml
services:
    App\Service:
        # Prepend with "@" to differentiate between service and function.
        factory: '@app\Factory\ServiceFactory'
        arguments: [ '%kernel.debug%' ]
```

```xml
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://symfony.com/schema/dic/services
               http://symfony.com/schema/dic/services/services-1.0.xsd">
    <services>
        <!-- ... -->
        <service id="App\Service"
                 class="App\Service">
            <factory service="App\Factory\ServiceFactory" />
        </service>
    </services>
</container>
```

```php
<?php

use App\Service;
use App\Factory\ServiceFactory;
use Symfony\Component\DependencyInjection\Reference;

$container->register(Service::class, Service::class)
    ->setFactory(new Reference(ServiceFactory::class));
```

Commits
-------

23cb83f [DependencyInjection] Invokable Factory Services

…dwin)

This PR was merged into the master branch.

Discussion
----------

[DependencyInjection] Invokable Factory Services

Document new invokable factories (and configurators) implemented in symfony/symfony#30255.

There are now four ways to reference factories, perhaps making them more clear might be something else to do.
- `function`
- `Class::method`
- `Service:method`
- `@InvokableService`

Commits
-------

2d7709f [DependencyInjection] Invokable Factory Services