Fix Navigation Bar Elements ignoring State variables.

[alexmodrono]

• I have checked that nobody else has reported this issue.
• I know that I'm reporting a bug for Codename Starlight (SwiftUI) and not for Hyperspace Desktop (JS).

Describe the bug
A clear and concise description of what the bug is.

When creating a navigation bar element, there are many times where you want it to change depending on a specific variable. The problem with this is that, since navigation bar elements are passed through preference keys, for some reason they seem to ignore state variable updates, and, as a result, do not change.

[alexmodrono]

Assigning this the enhancement tag since fixing this requires more than just a PATCH because we need to change the way StylableScrollView works in a way that is not backward-compatible, so it requires a MAJOR update.

This also means that this change provides direct customer value because StylableScrollView now provides a new way for adding navigation bar elements that allow for more customization.

[alexmodrono]

Fixed by #3.