[Sync EN] ext/dom: Document the new Dom\ParentNode $children property (PHP 8.5) (#5677)

Commit: `https://github.com/php/doc-en/commit/34314b7c6eab4d9b7efabd42154b38fcc5db1fef`
PR: `https://github.com/php/doc-en/pull/5677`

**Neue EN-Dateien (noch nicht übersetzt)**
- `reference/dom/dom/dom-document.xml`
- `reference/dom/dom/dom-documentfragment.xml`
- `reference/dom/dom/dom-element.xml`
- `reference/dom/dom/dom-parentnode.xml`
