[Bug]: Multi-level sideNav does not convey structure

[jnurthen]

Code of conduct

• [X] I agree to follow this project's code of conduct.

Impacted component(s)

sp-sidenav

Expected behavior

Mutli-level sidenav should convey the level to AT. The easiest way to do this is nested lists

Actual behavior

No level information is conveyed to AT

Screenshots

No response

What browsers are you seeing the problem in?

Firefox, Chrome, Safari, Microsoft Edge

How can we reproduce this issue?

1. Go to https://opensource.adobe.com/spectrum-web-components/components/sidenav/#multi-level
2. Look at structure - no level information is conveyed.
3. Confirm using NVDA or VO. The structure is not conveyed

Sample code that illustrates the problem

https://opensource.adobe.com/spectrum-web-components/components/sidenav/#multi-level

Logs taken while reproducing problem

No response