Implement a DOT subset as the type system for Orc

[arthurp]

This issue tracks the plan of for building an Orc type system based on Dependent Object Types (see 10.1145/3022671.2984008).

• [x] Study the DOT system (see the attached paper) to determine how hard it will be to write a type checker (not inferencer) for the full system and determine what subset of the language to support in the type checker. The point is to select a subset which we can implement quickly (within a week or two).
• [x] Update the Orc IRs to match the required type annotations and allowed syntactic forms. The largest of these changes will be to remove the "new C" form of object construction from the IR (it will still exist at the surface language) and replace it with an encoding that I have already designed and written up.
• [ ] Implement the selected subset of DOT in the type checker.
• [ ] Implement basic type inference. This will make no attempt to match even Scala's level of type inference. It should be able to reuse what we already have in the old Orc type checker. We will only implement the lowest hanging fruit.

Once this work is complete it should address issues #165 and #170. It may also address #167 and #168.

PS: This would be a project board except there is an arbitrary restriction on the length of notes on project boards which is so stupid I decided not to deal with it. This is still a proposal for changes in the repo, so it's not too far from what issues are for.

[arthurp]

I have written a document describing what I think is the first step for implementing DOT in Orc. It also describes how path-dependent types could be implemented later in Orc.

https://orc.csres.utexas.edu/wiki/Wiki.jsp?page=RestrictedDOTForOrc

[arthurp]

As of 584b16de2e63c0267fbfd14a745352d95a102e35, the untyped element of this is working. There are still things that need to be done to allow typing (Some types generated by the translator are still placeholders). I have added todos marked "TODO: TYPECHECK". In addition, the current translator and parser do not support type members or nested classes at all.