Function emit_mermaid_constraint_graph 

fn emit_mermaid_constraint_graph<'tcx>(
    borrow_set: &BorrowSet<'tcx>,
    liveness: &LivenessValues,
    localized_outlives_constraints: &[LocalizedOutlivesConstraint],
    out: &mut dyn Write,
) -> Result<usize>

Emits a mermaid flowchart of the polonius localized outlives constraints, with subgraphs per region, and loan introductions.