Is your feature request related to a problem? Please describe.
In causal graphs (DAG, ADMG, CPDAG, PAG, MAG), there is the notion of an edge being visible. For the DAG/ADMG/CPDAG, edges are by definition always visible.

Describe the solution you'd like
Implement function visible_edge(graph, source, target) to determine if the edge between source and target is visible or not.

One can follow the papers https://auai.org/uai2015/proceedings/papers/155.pdf and https://www.jmlr.org/papers/volume18/16-319/16-319.pdf, and figures to use as unit-test cases.

Additional context
py-why/dowhy#402 (comment)