Add a control-flow graph viewer

[aeisenberg]

The use case of the control-flow graph viewer is for teams developing language libraries. They need to ensure that the CFG generated by the CodeQL library is correct. In particular, such a graph makes it easy to see erroneously disconnected components.

The CFG does not need to span across files.

[naveedgazi]

Any updates on this feature? Having the ability to view CFGs for source code would be immensely useful.

[aeisenberg]

We haven't prioritized this work yet. This is not a straightforward feature to implement well. Control flow graphs can be large and complex and most graph visualization libraries focus on smaller graphs that can be viewed on a single screen.

Some thought and care needs to go into creating a graph viewer that is easy to understand and complete.