Returns the signed area of the specified polygon. If the vertices of the polygon are in counterclockwise order
(assuming a coordinate system where the origin <0,0> is in the top-left corner), the returned area is positive;
otherwise it is negative, or zero.
Parameters
polygon: [number, number][]
Array of coordinates <x0, y0>, <x1, y1> and so on.
Returns the signed area of the specified polygon. If the vertices of the polygon are in counterclockwise order (assuming a coordinate system where the origin <0,0> is in the top-left corner), the returned area is positive; otherwise it is negative, or zero.