getTileById(tileId, x, y) {
		if (!this.tileset.contains(tileId)) {
			// look for the corresponding tileset
			this.tileset = this.tilesets.getTilesetByGid(tileId);
		}
		return new Tile(x, y, tileId, this.tileset);
	}
return a new the Tile object corresponding to the given tile id
@param {number} tileId - tileId
@param {number} x - X coordinate (in world/pixels coordinates)
@param {number} y - Y coordinate (in world/pixels coordinates)
@returns {Tile} the tile object