addFloat32 method
Add the field with the given 32-bit float value.  The field
is not added if the value is equal to def.
Implementation
void addFloat32(int field, double? value, [double? def]) {
  assert(_inVTable);
  if (value != null && value != def) {
    _prepare(_sizeofFloat32, 1);
    _trackField(field);
    _setFloat32AtTail(_tail, value);
  }
}