… to assist in writing and discovering app's configuration (nicolas-grekas)

This PR was squashed before being merged into the 7.4 branch.

Discussion
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[FrameworkBundle] Auto-generate `config/reference.php` to assist in writing and discovering app's configuration

| Q             | A
| ------------- | ---
| Branch?       | 7.4
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Doc PR | symfony/symfony-docs#21511
| License       | MIT

This PR reverts #61490 and #61885, and builds on #61894.
These reverts explain a big chunk of the attached patch.

This adds a compiler pass that generates a `config/reference.php` file.
This file contains two classes that define array-shapes for app's and routing configuration.
Part of these shapes are auto-generated from the list of bundles found in `config/bundles.php`.

The `config/reference.php` file should be loaded by a new line in the "autoload" entry of composer.json files: `"classmap": ["config/"]` - recipe update pending. This means that the file should be committed. This is on purpose: as the name suggests, this file is also a config reference for human readers. Having to commit the changes is also a nice way to convey config improvements to the community - at least for ppl that review their commits ;). It also solves a discovery problem that happens with phpstan/etc having a hard time to find the classes currently generated for config builders in the cache directory.

With this PR, `config/services.php` could start as such:

```php
<?php

namespace Symfony\Component\DependencyInjection\Loader\Configurator;

return App::config([
    'services' => [
        'App\\' => [
            'resource' => '../src/'
        ],
    ],
]);
```

and `config/routes.php` would start as:

```php
<?php

namespace Symfony\Component\Routing\Loader\Configurator;

return Routes::config([
    'controllers' => [
        'resource' => 'attributes',
        'type' => 'tagged_services',
    ]
]);
```

The generated shapes use advanced features that are not fully supported by phpstan / phpstorm. But the gap should be closed soon.

PS: https://symfony.com/blog/new-in-symfony-7-4-deprecated-xml-configuration will need an update.

Commits
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22349f5 [FrameworkBundle] Auto-generate `config/reference.php` to assist in writing and discovering app's configuration