Add IdentifierNode when either a Unit or Layered model.
Add IdentifierNode when either a Unit or Layered model.

uwdata/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,vega/vega-lite