Performance: Investigate and improve `HoverOverlay` performance (Spike)

[umpox]

Description

Goal: Render code intelligence faster

Reason:

• Particularly slow here, by default we only fetch code intelligence information on hover.
  • Ideally we could do this server side, although that might be a big task
  • Could we fetch all known symbols on load, and pre-populate those tokens ready to be used for hover overlays?
    • This would help accessibility, as we could make them buttons that are tabbable too.
    • This is essentially what the symbol sidebar does

[sourcegraph-bot-2]

Heads up @taylorsperry @jasongornall - the "team/frontend-platform" label was applied to this issue.