Update on "Implement aten::index | feat(torchlib) (#862)"

---

**This change implements the logic for `aten::index` and adds tests for different nd index combinations and permutations.**

## Understanding `aten::index`

For `arg0` with shape `[7, 3, 4, 5, 6]`
The indexing operation `arg0[0, :, 1:2, tensor([[4,5]])]` will be translated to
```
+>  select: i64[3, 4, 5, 6] = torch.ops.aten.select.int(arg0, 0, 0);
+>  slice_1: i64[3, 4, 5, 6] = torch.ops.aten.slice.Tensor(select, 0, 0, 9223372036854775807);
+>  slice_2: i64[3, 1, 5, 6] = torch.ops.aten.slice.Tensor(slice_1, 1, 1, 2);
+>  index: i64[3, 1, 1, 2, 6] = torch.ops.aten.index.Tensor(slice_2, [None, None, arg1]);
```
Here,
- `indices = [None, None, arg1]` is equivalent to `indices = [None, None, arg1, None]`
- The operation `arg0[0, :, 1:2, tensor([[4,5]])]` is equivalent to `arg0[0, :, 1:2, tensor([[4,5]]), :]`
None in `indices` are like fillers for dimensions that cannot be removed in the process.

## Gather op reference

- https://github.com/openxla/xla/blob/main/docs/operation_semantics.md?rgh-link-date=2023-07-13T01%3A09%3A16Z#gather
- https://www.pathpartnertech.com/gather-scatter-operation-in-deep-learning-framework/

---------

Co-authored-by: BowenBao <bowbaomicrosoft.com>

[ghstack-poisoned]

Author: justinchuby

onnxscript/tests/function_libs/torch_lib/extra_opinfo.py

@@ -460,6 +460,7 @@ def sample_inputs_index(op_info, device, dtype, requires_grad, **kwargs):
         ([None, None, None, index_1d],),
         ([index_1d, None],),
         ([index_1d, None, None],),
+        # Extra index
         ([None, index_1d, None, index_1d],),
         ([index_1d, None, index_1d, None],),
         ([None, index_1d, index_1d, None],),
@@ -468,6 +469,7 @@ def sample_inputs_index(op_info, device, dtype, requires_grad, **kwargs):
         ([None, None, None, index_2d],),
         ([index_2d, None],),
         ([index_2d, None, None],),
+        # Extra index
         ([None, index_2d, None, index_2d],),
         ([index_2d, None, index_2d, None],),
         ([None, index_2d, index_2d, None],),
@@ -476,11 +478,15 @@ def sample_inputs_index(op_info, device, dtype, requires_grad, **kwargs):
         ([None, None, None, index_3d],),
         ([index_3d, None],),
         ([index_3d, None, None],),
+        # Extra index
         ([None, index_3d, None, index_3d],),
         ([index_3d, None, index_3d, None],),
         ([None, index_3d, index_3d, None],),
         # Mixed indices
         ([None, index_3d, index_1d, index_2d],),
+        # All indices are not None
+        ([index_2d, index_3d, index_1d],),
+        ([index_2d, index_3d, index_1d, index_2d],),
     ]
 
     for args in test_args: