Add workspace functions to extension API

[alexweininger]

Goals:

• Expose the workspace methods that Limelight needs in the extension API.
• Provide typings for these APIs without exposing too much types from our own extension, that Limelight doesn't need

This got really messy so I ended up making some new types that are for the API, then some internal types that are only for our use. In the future if this becomes something that ends up being used a lot, we can clean it up. But it will require a lot of type refactoring and is not a small job.

[nturinski]