Determines if a point is inside a triangle.
Example:
// Returns true
const p = new Cesium.Cartesian2(0.25, 0.25);
const b = Cesium.pointInsideTriangle(p,
new Cesium.Cartesian2(0.0, 0.0),
new Cesium.Cartesian2(1.0, 0.0),
new Cesium.Cartesian2(0.0, 1.0));