Error Handling: propagate status for ReleaseGilAndTransferData and XlaDataToTensors.

[ysiraichi]

This PR refactors our error handling by replacing GetValueOrThrow with proper status propagation using absl::StatusOr<T> and XLA_ASSIGN_OR_RETURN macros.

Key Changes:

• ReleaseGilAndTransferData Function:

  • Updated the function signature to return absl::StatusOr<std::vector<xla::Literal>>.
  • Replaced GetComputationClientOrDie() with GetComputationClient().
  • Utilized XLA_ASSIGN_OR_RETURN for client acquisition and TransferFromDevice calls.
  • Updated callers in tensor_util.cpp and xla_graph_executor.cpp to handle the new StatusOr<T> return type.

• XlaDataToTensors Function:

  • Modified the function signature to return absl::StatusOr<std::vector<at::Tensor>>.
  • Replaced GetValueOrThrow with XLA_ASSIGN_OR_RETURN for the ReleaseGilAndTransferData call.
  • Updated all callers (including XLATensor::ToTensor, test_xla_sharding.cpp, init_python_bindings.cpp, and xla_backend_impl.cpp) to correctly handle the StatusOr<T> return type.
  • Added necessary status.h includes to xla_backend_impl.cpp and test_xla_sharding.cpp.

These modifications align with existing status propagation patterns in the codebase, as seen in pjrt_registry.cpp, and maintain API-level backward compatibility while improving internal error handling within the tensor conversion pipeline.

[zhanyong-wan]

Thanks!