message: Add support for importing CallOnce op attribute in the flatbuffer importer
diff: @@ -589,6 +589,12 @@ StatusOr<Operation*> BuildConstOp(const tflite::TensorT& tensor,
  llvm::SmallVector<mlir::NamedAttribute, 4> ConvertSubgraphIdxsToFunctionAttrs(
  tflite::BuiltinOptionsUnion options,
  const std::vector<std::string>& func_names, Builder builder) {
  + if (auto* opts = options.AsCallOnceOptions()) {
  + uint32_t init_idx = opts->init_subgraph_index;
  + auto init_attr = builder.getStringAttr(func_names.at(init_idx));
  +
  + return {builder.getNamedAttr("session_init_function", init_attr)};
  + }
  if (auto* opts = options.AsIfOptions()) {
  uint32_t then_idx = opts->then_subgraph_index;
  auto then_attr = builder.getSymbolRefAttr(func_names.at(then_idx));
  