Cache DHE Core+ jsapis by worker kind / engine type

[bmingles]

The extension currently stores Core+ jsapi downloads by worker URL. Some workers might use the same api version, so it would be more optimal to cache by worker kind / engine type to avoid duplicate downloads.

e.g. We do this in the web here:
https://github.com/deephaven-ent/iris/blob/0fccc395d44974571e71085c762b68c151c7ca58/web/client-ui/src/main/AppMainContainer.tsx#L587