Rib Robustness: Avoid Recursive algorithm of type-pull-up and use queue & stack

[afsalthaj]

No description provided.

[afsalthaj]

This is recursion currently because we bumped into Rust borrowing issues with the following efficient logic
which may require changing Expr data structure with RefCells.
Logic that we need:

• Fill up a queue with the parent node being first
  [select_field(select_field(a, b), c), select_field(a, b), identifier(a)]
  Pop from back and push to the front of a stack of the current expression's inferred type, and keep assigning it.
  Example:
• Pop back to get identifier(a)
• Try to pop_front inferred_type_stack, and if its None. Push front the identifier(a)'s inferred_type: Record(b -> Record(c -> u64))
• Pop back from stack to get select_field(a, b)
• Try to pop_front inferred_type_stack, and its Record(b -> Record(c -> u64)). Get the type of b and assign itself and push_front to stack.
• Pop back from stack to get select_field(select_field(a, b), c)
• Try to pop_front inferred_type_stack, and its Record(c -> u64). Get the type of c and assign itself and push to stack.

[afsalthaj]

@jdegoes I would like a pair up to implement this or similar in Rust without changing Expr data structure. With changing Expr to RefCell (may Rc-RefCell I can see it working though. May be there is a better way that you may have an idea.