Cleanup

* Use JSDoc when possible
* Switch return types from Language Service public APIs to interfaces
* remove unused files
* remove references to 'foo' from user facing messages
You might disagree, but what do you think of turning these into multiline JSDoc comments?

I think you should be able to find/replace easily with:
VS Search Regex: `(\s+)\*\* (.+) \*/`
VS Replacement String: `$1/**\r\n$1 * $2\r\n$1*/`