Consider adding graph visualization utility for constraint graph

It's difficult to examine the algebraic graph built in the IR by just printing the nodes of the graph. So, some visualization utility would be useful to debug or examine the constraint graph while we don't have unit tests for IR. This utility could also be useful for users writing constraints in AirScript to visually examine the constraints finally produced.

There could be other ways to make life easier for contributors and users rather than graph visualization and should be explored more.