Fix broken indexing when using None and ellipses indexing together (#22905)
Summary:
https://github.com/pytorch/pytorch/issues/20153
I believe you need 2 passes for this. Take this example
```python
torch.jit.script
def f():
x = torch.ones(10, 9, 8, 7, 6)
return x[..., None, None].shape
```
which results in `[10, 9, 8, 7, 6, 1, 1]`
vs
```
torch.jit.script
def f():
x = torch.ones(10, 9, 8, 7, 6)
return x[..., None, None, :].shape
```
which results in `[10, 9, 8, 7, 1, 1, 6]`
After only processing `x[..., None, None` we don't know whether we should be creating a new dimension at the end of the dimension list or somewhere in the middle. What we do depends on the elements to the right of it.
Thus, I do 2 passes - one to collect all the dimensions that the index operations operate on, and another that executes the index operations.
This still doesn't work for an ellipse index followed by a tensor index, but it wasn't working previously either.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22905
Differential Revision: D16433558
Pulled By: Chillee
fbshipit-source-id: c1b303cb97b1af8b6e405bad33495ef3b4c27c4a
