Function reverse_arc_ring

pub fn reverse_arc_ring(ring: &ArcRing) -> ArcRing

Reverse an arc ring in place, preserving its arcs.

Reversing the vertex order alone is NOT enough: a bulge belongs to the edge LEAVING its vertex, so after reversal each vertex must take the negated bulge of what was previously its predecessor. Getting this wrong flips every arc to the wrong side while the ring still closes.