Fix lifting constants (#1862)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1862

ScalarToTensorPass which is run as an aten_to_edge_pass lifts all scalars in the graph to tensors. However this breaks the contract that all constant tensors should be lifted as inputs. To fix this, we can move the lift_constants_pass to after the ScalarToTensorPass.

Reviewed By: cccclai

Differential Revision: D53454481

fbshipit-source-id: 2aca505da7cc678d891fe7630fba4090e12414be