simple ui: add back search reference panel (again)
Created by: limitedmage
Closes #40998 (closed) (again) The original PR, #41005, was broken due to a merge conflict from a large refactor done on the sidebar.
(review with "hide whitespace" enabled)
Test plan
Verify that the reference panel is shown whether Simple UI is on or off.
App preview:
Check out the client app preview documentation to learn more.