Make workspace item testing easier

[hojberg]

There should be some nice test helpers to create workspace items of various kinds to enable a better testing story.
It is quite difficult to construct a WorkspaceItem since it relies on hashes (that can only be constructor with a function that returns a maybe), non empty syntax and a lot of other details that may or may not be interesting to the test.

One way to deal with this could be to create a smart constructors for terms and types.