feat: add notion of parent/child in the menu data structures

[MarvinKlein1508]

🙋 Feature Request

The FluentNav component should know which child items are active to expand the navigation bar correctly when browsing the page through a bookmark or external link.

🔦 Context

Related to #2297 & #2142

[vnbaaij]

This is going to take a significant amount of work, I believe. We will investigate for the next major version