Function incircle

incircle(
    ax: number,
    ay: number,
    bx: number,
    by: number,
    cx: number,
    cy: number,
    dx: number,
    dy: number,
): number
The points a, b, and c must be in counterclockwise order, or the sign of the result will be reversed.
Parameters
- ax: number
  x coordinate of first point
- ay: number
  y coordinate of first point
- bx: number
  x coordinate of second point
- by: number
  y coordinate of second point
- cx: number
  x coordinate of third point
- cy: number
  y coordinate of third point
- dx: number
  x coordinate of fourth point
- dy: number
  y coordinate of fourth point
Returns number
- a positive value if the point d lies outside the circle passing through a, b, and c.
- a negative value if it lies inside.
- zero if the four points are cocircular.