Visitor responsible for traversing a bytecode basic block map and building a control flow graph (CFG).
The primary purpose of this transformation is to create a CFG, which is used by later transformers for dataflow analysis.
Given a bytecode flow, and an optional number of arguments, return a llpython.control_flow.ControlFlowGraph instance describing the full control flow of the bytecode flow.
Given a Python function, create a bytecode flow, visit the flow object, and return a control flow graph.