Evaluate switch to symfony/dotenv

If features are the same and perfs are better, switch.

• https://github.com/drupal-composer/drupal-project/issues/379
• https://github.com/vlucas/phpdotenv/issues/549
• https://www.reddit.com/r/PHP/comments/durgf4/performance_issues_with_vlucasphpdotenv/?tl=fr