Type inference features

[asgerf]

Tracking issue for missing type inference features, not including minor fixes, and in no particular order.

Soundness:

• [ ] Handle objects with user-defined noSuchMethod
• [x] Handle objects with user-defined call method
• [ ] Handle and/or bailout on dart:mirror usage
• [ ] Get fine-grained external method behavior from file or metadata
• [ ] Get entry point specification from file

Precision:

• [x] Track bitmask with nullability and other particularly important values
• [ ] Integrate with strong mode
• [ ] Join closures using function signature
• [ ] Specialize generics
• [ ] Generate proper lattice using intersection types, to ensure iteration order-independence
• [x] Track base information
• [ ] Distinguish integers and doubles in arithmetic
• [ ] Perform tree-shaking analysis: do not analyze unreachable code

Tooling:

• [x] Transformation to dynamically check correctness inference results
• [ ] Better visualization of constraint system
• [ ] Backtracking tool for understanding results of inference