function vornoiRegion(line, point) {
	const len2 = line.length2();
	const dp = point.dot(line);
	if (dp < 0) {
		// If the point is beyond the start of the line, it is in the
		// left vornoi region.
		return LEFT_VORNOI_REGION;
	} else if (dp > len2) {
		// If the point is beyond the end of the line, it is in the
		// right vornoi region.
		return RIGHT_VORNOI_REGION;
	} else {
		// Otherwise, it's in the middle one.
		return MIDDLE_VORNOI_REGION;
	}
}
Calculates which Vornoi region a point is on a line segment. <br>
It is assumed that both the line and the point are relative to `(0,0)`<br>
<pre>
            |       (0)      |
     (-1)  [S]--------------[E]  (1)
            |       (0)      |
</pre>

@ignore
@param {Vector2d} line - The line segment.
@param {Vector2d} point - The point.
@returns  {number} LEFT_VORNOI_REGION (-1) if it is the left region,
         MIDDLE_VORNOI_REGION (0) if it is the middle region,
         RIGHT_VORNOI_REGION (1) if it is the right region.