message: Add source positions to `const` operations
diff: @@ -131,6 +131,8 @@ class JSONTransformer(lark.Transformer):
  }
  if type:
  out['type'] = type
  + if self.include_pos:
  + out['pos'] = {'row': dest.line, 'col': dest.column}
  return out
  def vop(self, items):
  