Refactor context switcher items lists

What does this MR do and why?

This refactors the context switcher's items lists to make it easier to differentiate between frequently used items and search results. This greater differentiation will allow us to easily add feature to one list without affecting the other. For example, we need to make search results collapsible, but not frequent items, which would be a pain if both things were being rendered by the same component.

Screenshots or screen recordings

No visual change.

How to set up and validate locally

1. Enable the new nav:

   1. Enable the feature flag:

      echo "Feature.enable(:super_sidebar_nav)" | rails c

   2. Enable the user setting from the user dropdown:

      

2. In the super sidebar, click on the context title to expand the context switcher.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #378541 (closed)