Improve hierarchical layout for graphs with mixed-directional flow

[mitchmindtree]

In the case that some nodes flow top-down, and some nodes flow left-to-right, the existing layout approach will give undesirable results as it assumes the whole graph is laid out in a particular direction.

We should probably do something like the following:

1. Remove edges that connect nodes with different flow directions.
2. Collect the SCCs on the remaining graph.
3. Layout each SCC independently.
4. Determine the bounding boxes for the resulting SCC layouts.
5. Connect the SCCs that were previously connected before edge removal.
6. Layout the outer graph of SCCs using their bounding boxes.
   • Not sure how to pick a direction preference here? Make it optional I guess?