extract `scale._useRawDomain()` to simplify the code and refer to field correctly when `useRawDomain` is activated.
extract `scale._useRawDomain()` to simplify the code and refer to field correctly when `useRawDomain` is activated.

Fixes https://github.com/vega/voyager/issues/207

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