This function works by first checking if full_token is of the form
object, package::object or package:::object. In the first two cases,
it will look into all exported objects of loaded packages (or just package
for the second case) and return any mathching objects. For the last case,
it will look at the unexported objects of package.
workspace_completion(workspace, full_token)a Workspace object
a character, the object to identify
a list of candidates