Separate `ModelToHeader.cpp` into 3 different files:
1. DependencyGraph, used to calculate the precedence between
type declarations
2. ModelTypeNames, that holds all the naming logic, whose
primitives are accessible from other modules through a
public header
3. ModelToHeader, that now contains only the logic to print
out declarations and definitions
Also add a compilation test for the headers generated by this pass.
Pietro Fezzardi