Call graph edges should have a branch indicator and a popup branch selector

[tlatoza]

Edges in the call graph that execute more than once should have an indicator showing the number of executions and which execution is currently selected, in the same way as code in the code editor. Hovering over this indicator brings up the branch selector popup.

[tlatoza]

Example: https://seecode.run/#-KY-onw1le4g9DWIiCed