Implement type system for Bend

[kings177]

#615 describes the need for having a type system for Bend as well as the design discussion of how this system should be.

This issue tracks the implementation of the bend type system.

• [x] Compile bend programs to kindc, deferring type checking to kind.
• [x] Study the implementation of Hindley-Milner type systems.
• [x] Search for extensions and alternatives to HM that could allow for a less restrictive set of accepted lambda terms.
• [x] Implement a simple HM type system with type inference.
• [x] Add recursion to the type system.
• [x] Add adts to the type system.
• [x] Add mutual recursion to the type system.
• [x] Port the type system from haskell to rust.
• [x] Port the implemented type system to Bend.
• [x] Add the Bend-specific types to the type system (numbers, tuples, None).
• [x] Add type checking, comparing with user provided annotations.
• [x] Add non-checked functions.
• [x] Add the untyped type Any.
• [x] Write good type error diagnostics.
• [x] Update the builtin library to use the new type system correctly.
• [x] Write tests for type inference and type checking.