[4.4] Adminmenu: Fix export for child items

[Hackwar]

Pull Request for Issue #37273 .

Summary of Changes

When exporting a menu preset in J4, the information about the tree of the menu items gets lost. This fixes that.

Testing Instructions

1. Go to menu manager, filter by admin and create a new menu for the administrator. Make sure to select a preset to pre-populate the menu.
2. In the menu manager, select the menu and click "Download as Preset"

Actual result BEFORE applying this Pull Request

You get a XML in return and all <menuitem> tags are on the same level.

Expected result AFTER applying this Pull Request

The menuitem tags are nested properly in the way they are in the menu tree.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[brianteeman]

I have tested this item ✅ successfully on a4eb988

---

_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43178.}

[Quy]

I have tested this item ✅ successfully on a4eb988

---

_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43178.}

[Quy]

RTC

---

_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43178.}

[MacJoom]

Thank you!