message: Add int16 support for Pack on GPU
  This fix tries to add int16 support for Pack on GPU,
  so that the issue raised in 20370 could be addressed.
  This fix is related to 20370.
diff: @@ -158,7 +158,8 @@ REGISTER_PACK(string);
  TF_CALL_GPU_NUMBER_TYPES(REGISTER_GPU);
  TF_CALL_bfloat16(REGISTER_GPU);
  TF_CALL_int64(REGISTER_GPU);
  -REGISTER_GPU(bool);
  +TF_CALL_int16(REGISTER_GPU);
  +TF_CALL_bool(REGISTER_GPU);
  #undef REGISTER_GPU
  // A special GPU kernel for int32.
  