Import Cryptol enum types as SAWCore datatypes

[brianhuffman]

WIP

[brianhuffman]

The only important test failure is in test3305, introduced in #3307, which tests the support for derived Eq, Cmp and SignedCmp instances for Cryptol enum types.

This PR won't be ready until I implement class dictionaries for enum-derived datatypes. One way to do it would be to define a special "representation" function for each datatype that converts it to the old-style nested-eithers-and-products form. Then we could reuse the existing dictionary constructors added in #3307, and lift them to the datatypes using the rep function.

[RyanGlScott]

How is the namespacing for Cryptol-imported enums handled? For instance, if you import two enums named E, one from module A and another from module B, are they disambiguated?

This PR won't be ready until I implement class dictionaries for enum-derived datatypes. One way to do it would be to define a special "representation" function for each datatype that converts it to the old-style nested-eithers-and-products form. Then we could reuse the existing dictionary constructors added in #3307, and lift them to the datatypes using the rep function.

That would work, although I'd be a bit sad to have to still rely on the sum-of-products even after switching to a SAWCore datatype representation---the latter was supposed to subsume it!