Collect rules in definition order for export to CDDL

As with all languages, we may sometimes want to group related definitions together when doing helps to understand the semantics of what's being written. At the moment, collecting CDDL definitions from a file has no knowledge of the definition order, since this is opaque to Haskell at the surface level.

Perhaps some TH stuff would work.

Start by locating the code that collects CDDL definitions from a file and examining how the Haskell surface currently loses definition order. Investigate whether Template Haskell can preserve that order; done means exported CDDL rules retain the order in which definitions appear in the source.

Written by the indexing model from the issue text.