Add DirectionalLight to the selection of 3D light types

Summary

Add a DirectionalLight to the JavaFX 3D API.

Problem

JavaFX contains only an AmbientLight, a PointLight and a SpotLight. A DirectionalLight is a common light that isn't provided by JavaFX currently.

Solution

Add a DirectionalLight implementation.

Specification

/**
 * A light that illuminates an object from a specific direction.
 * The direction is defined by the {@link #directionProperty() direction} vector property of the light. The direction
 * can be rotated by setting a rotation transform on the {@code DirectionalLight}. For example, if the direction vector is
 * {@code (1, 1, 1)} and the light is not rotated, it will point in the {@code (1, 1, 1)} direction, and if the light is
 * rotated 90 degrees on the y axis, it will point in the {@code (1, 1, -1)} direction.
 * <p>
 * {@code DirectionalLight}s can represent strong light sources that are far enough from the objects they illuminate
 * that their light rays appear to be parallel. Because these light sources are considered to be infinitely far, they
 * cannot be attenuated. A decrease in intensity can be achieved by using a darker color. The sun is a common light
 * source that can be simulated with this light type.
 *
 * @since 18
 * @see PhongMaterial
 */
public class DirectionalLight extends LightBase {

    /**
     * Creates a new {@code DirectionalLight} with a default {@code Color.WHITE} color.
     */
    public DirectionalLight()

    /**
     * Creates a new {@code DirectionalLight} with the specified color.
     *
     * @param color the color of the light source
     */
    public DirectionalLight(Color color)

    /**
     * The direction vector of the directional light. It can be rotated by setting a rotation transform on the
     * {@code DirectionalLight}. The vector need not be normalized.
     *
     * @defaultValue {@code Point3D(0, 0, 1)}
     */
    public final ObjectProperty<Point3D> directionProperty() 

    public final void setDirection(Point3D value) 

    public final Point3D getDirection()
}