orient
the orientation of a non-stacked bar, area, and line charts.
The value is either "horizontal", or "vertical" (default). For bar and
tick, this determines whether the size of the bar and tick should be
applied to x or y dimension. For area, this property determines the
orient property of the Vega output. For line, this property determines
the path order of the points in the line if path channel is not specified.
For stacked charts, this is always determined by the orientation of the stack;
therefore explicitly specified value will be ignored.