Returns the signed area of the polygon using the shoelace formula.
The result is positive when the vertices wind counter-clockwise and negative
when they wind clockwise, so the sign can be used to determine winding order.
Parameters
vertices: number[]
polygon vertices as a flat array [x0, y0, x1, y1, ...]
Returns the signed area of the polygon using the shoelace formula. The result is positive when the vertices wind counter-clockwise and negative when they wind clockwise, so the sign can be used to determine winding order.