[Sync EN] Add a warning about the subtle global state in legacy random functions

PR: `https://github.com/php/doc-en/pull/5414` (2026-03-23)

**Fichiers FR à mettre à jour**
- `language-snippets.ent`
- `reference/array/functions/array-rand.xml`
- `reference/array/functions/shuffle.xml`
- `reference/random/functions/mt-rand.xml`
- `reference/random/functions/rand.xml`
- `reference/strings/functions/str-shuffle.xml`

