feature #46564 [DependencyInjection] Add Enum Env Var Processor (jack-worman)

This PR was merged into the 6.2 branch.

Discussion
----------

[DependencyInjection] Add Enum Env Var Processor

| Q             | A
| ------------- | ---
| Branch?       | 6.2
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | N/A
| License       | MIT
| Doc PR        | waiting on approval of feature

Add the ability to transform env variables into \BackedEnums.

For example, you could now autowire an enum from an environment variable:
```php
<?php

use Symfony\Component\DependencyInjection\Attribute\Autowire;

enum AppEnv: string {
   case Test = 'test';
   case Dev = 'dev';
   case Stage = 'stage';
   case Prod = 'prod';
}

class Foo {
    public function __construct(
        #[Autowire('%env(enum:'.AppEnv::class.':APP_ENV)%')]
        private AppEnv $appEnv,
    ) {}
}
```

Commits
-------

41e22723c4 Add Enum Env Var Processor

Author: nicolas-grekas

DependencyInjection/FrameworkExtension.php

@@ -1722,7 +1722,7 @@ private function registerSecretsConfiguration(array $config, ContainerBuilder $c
         }
 
         if ($config['decryption_env_var']) {
-            if (!preg_match('/^(?:[-.\w]*+:)*+\w++$/', $config['decryption_env_var'])) {
+            if (!preg_match('/^(?:[-.\w\\\\]*+:)*+\w++$/', $config['decryption_env_var'])) {
                 throw new InvalidArgumentException(sprintf('Invalid value "%s" set as "decryption_env_var": only "word" characters are allowed.', $config['decryption_env_var']));
             }