ATR-21896 : Add back vertex building even when no conversions

For some reason Legacy Trigger can attempt vertex building even with conversions disabled.

So lets leave / put back the doVertexBuilding flag to control this , independently of doConversion.

i.e reintroduce splitting of doVertexBuilding doConversion flags.

I honestly do not have traced the coupling of these 100% but seems to be there, and is not obvious yet to me where it comes from ...