[Tiled] Add Parallax Factor in TiledMapLayer (New in Tiled 1.5)

[fossegutten]

Add a Vector2 property for the new Parallax Factor property in TiledMapLayer class.

[fdrobidoux]

This shouldn't be too hard :

• Add a Vector2 ParallaxFactor property to TiledMapLayer
• Extract it from the tiled map file during reading.
• Add it to the TiledMapLayer during processing.

The rest could be handled by the user for now, like this for example, using an OrthographicCamera :

foreach (var tiledMapLayer in _tiledMap.Layers)
{
    _tiledMapRenderer.Draw(tiledMapLayer, _camera.GetViewMatrix(tiledMapLayer.ParallaxFactor));
}