Improve extruded PolygonGeometry with perPositionHeight

[hpinkos]

PolygonGeometry assumes the points with perPositionHeight are on the top, so when the extrudedHeight is greater than the position heights, the shape is inside out.

var viewer = new Cesium.Viewer('cesiumContainer');
var scene = viewer.scene;

var positions = Cesium.Cartesian3.fromDegreesArrayHeights([
    -108.0, 25.0, 100000,
    -100.0, 25.0, 100000,
    -100.0, 30.0, 100000,
    -108.0, 30.0, 300000
]);

var orangePolygonInstance = new Cesium.GeometryInstance({
    geometry : Cesium.PolygonGeometry.fromPositions({
        positions : positions,
        extrudedHeight: 400000,
        vertexFormat : Cesium.PerInstanceColorAppearance.VERTEX_FORMAT,
        perPositionHeight : true
    }),
    attributes: {
        color: Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.ORANGE)
    }
});

scene.primitives.add(new Cesium.Primitive({
    geometryInstances : orangePolygonInstance,
    appearance : new Cesium.PerInstanceColorAppearance({
        closed : true,
        translucent : false
    })
}));

Found in #2923

Bonus: it might be neat to be able to specify a top and bottom height per position.

[hpinkos]

Also reported here: https://groups.google.com/forum/#!searchin/cesium-dev/paula%7Csort:relevance/cesium-dev/FiF8tbgoPjw/ZXHBhlhABAAJ

[hpinkos]

Also reported in #8416