Quantity type item control has wrong value type

Calculations like ` %QuestionnaireResponse.item.where(linkId='height').answer.valueQuantity.value / 100` fails in sdc-ide, but works in fhir-emr
It happens because value is string, but it should be number

```
item:
  - linkId: height
    answer:
      - valueQuantity:
          value: '9'
          unit: cm
          system: http://unitsofmeasure.org
          code: cm
```

