feat(sidenav): add collapse support [khcp-17790]

[kaiarrowood]

Summary

Add expand/collapse support to sidenav groups for KHCP-17790.

[adamdehaven]

I realize this is still a draft, but wanted to provide some feedback early

[adamdehaven]

With the flag enabled, the spacing here (red area) increases more than it should. Can you compare with the flag off and adjust?

I believe the code looks good based on my previous review and our discussion but I'll take another look shortly on the code review

[adamdehaven]

Can you update the focus state (keyboard nav) of the collapse triggers to more closely match the item focus-visible state? I believe we're using some navigation design tokens if you look at the current implementation for the sidebar items

[adamdehaven]

question: when users expand/collapse items manually, and then navigate to another MFE app, the collapse state will be reset. Are we planning to keep this consistent via logic in the App Shell?

[adamdehaven]

For the menu on mobile, would it make sense to automatically expand all items at smaller viewports? (I can show you a way to do this via JS if needed)

Issues addressed