E-Graph Visualization

[marcusrossel]

Egg can generate dot/svg/png-files for its e-graphs. Try using the proofwidgets package to display this in the info-view.

[marcusrossel]

leanprover-community/ProofWidgets4#60

https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/A.20widget.20to.20display.20output.20from.20.60dot.60