private static void addInputColumnsToList(ShapeDetails shape,
      ArrayList<String> fieldNames, ArrayList<ObjectInspector> fieldOIs) {
    StructObjectInspector OI = shape.getOI();
    for (StructField f : OI.getAllStructFieldRefs()) {
      fieldNames.add(f.getFieldName());
      fieldOIs.add(f.getFieldObjectInspector());
    }
  }
For each column on the input RR, construct a StructField for it
OI is constructed using the list of input column names and
their corresponding OIs.

@param rr
@return
ql/src/java/org/apache/hadoop/hive/ql/parse/PTFTranslator.java