message: Add offsetData() function to cardinality policies to return pointer to underlying offsets array
diff: @@ -104,6 +104,10 @@ struct ConstantCardinality
  return m_begins[fromPos];
  }
  + IndirectionPtrType offsetData() { return m_begins.data(); }
  +
  + const IndirectionPtrType offsetData() const { return m_begins.data(); }
  +
  void bindBeginOffsets(ElementType fromSetSize, ElementType stride)
  {
  m_begins = typename BeginsSet::SetBuilder().size(fromSetSize).stride(stride);
  @@ -169,6 +173,10 @@ struct VariableCardinality
  return m_begins[fromPos];
  }
  + IndirectionPtrType offsetData() { return m_begins.data(); }
  +
  + const IndirectionPtrType offsetData() const { return m_begins.data(); }
  +
  ElementType totalSize() const
  {
  return m_begins.empty() ? ElementType() : offset(m_begins.size() - 1);
  