[JIT] Peephole optimize list ops (#37612)
Summary:
Peephole optimize `len(li)` and `li[index]` patterns.
This changes the Profiled Graph IR for the following tests:
```
(Test Name, Num ifs loops, Num non-tensor nodes)
Before:
('test_nn_Conv1d_reflect_stride2_pad2', 3, 14)
('test_nn_Conv2d_reflect_stride2_pad2', 3, 14)
('test_nn_Conv1d_circular_stride2_pad2', 5, 31)
('test_nn_Conv2d_circular_stride2_pad2', 5, 31)
('test_nn_Conv3d_circular_stride2_pad2', 5, 31)
('test_nn_Conv1d_replicate_stride2_pad2', 3, 14)
('test_nn_Conv2d_replicate_stride2_pad2', 3, 14)
('test_nn_Conv3d_replicate_stride2_pad2', 3, 14)
After
('test_nn_Conv1d_reflect_stride2_pad2', 0, 2)
('test_nn_Conv2d_reflect_stride2_pad2', 0, 2)
('test_nn_Conv1d_circular_stride2_pad2', 0, 4)
('test_nn_Conv2d_circular_stride2_pad2', 0, 7)
('test_nn_Conv3d_circular_stride2_pad2', 0, 10)
('test_nn_Conv1d_replicate_stride2_pad2', 0, 2)
('test_nn_Conv2d_replicate_stride2_pad2', 0, 2)
('test_nn_Conv3d_replicate_stride2_pad2', 0, 2)
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37612
Differential Revision: D21352676
Pulled By: eellison
fbshipit-source-id: f8a0e7653b7a6a4c769f075de9b3044242ca9336
