Build generic data-flow and abstract values #17

Generic data-flow infrastructure shared by every later analysis.

• Lattice API: bottom, top, join, partial order
• Worklist solver (forward and backward) over the CFG
• AbstractValue with constants, types and truthiness; taints, ranges, string constraints and nullability join with their analyses (Phases 5 and 8)
• Constant propagation as the reference client validating the Analysis Manager end to end

Reference: docs/architecture.md §18 Abstract Value Engine, §37 dataflow/ and abstract/.

Delivery: #18