This uses the new GlobalID scalar types in the Snippets code. The
benefits of this are:

- More informative types. A reader of our schema, or our queries can see
  what a valid value will be.
- Safer resolution and mutation. When using this type we guarantee that
  our code will only encounter valid values, from our own namespace, and
  when using the parameterized IDs, that they cannot refer to other
  kinds of object.