[Twig][Form] Moved twig.form.resources to a higher level

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #11296
| License       | MIT
| Doc PR        | In progress...
You can add a normalizer (on the $rootNode) which checks if `['form']['resources']` is set, and call a closure which merges the configurations into form_theme.

```php
->beforeNormalization()
    ->ifTrue(function ($v) { return count($value['form']['resources']) > 0; })
    ->then(function($v) {
        $v['form_themes'] = array_unique(array_merge($config['form']['resources'], $config['form_themes']));
       
        return $v;
    })
->end()
```