Implement TensorList and demonstrate it via Stack op (#73758)
This is part 1 of 2:
1) add TensorList op to LTC and implement TS lowering; Demonstrate with hand-implemented Stack Op
2) codegen support for TensorList, and move Stack Op to codegen
This should also unblock enabling the amp_foreach.. ops - (possible to do manually after (1), may need additional codegen support for inplace handling after (2))
