Support Python Slice class in TorchScript (#44335)
Summary:
Implements support for[ Python Slice class](https://docs.python.org/3/c-api/slice.html) (not slice expression, which is already supported)
Slice object can be used in any place that supports slice expression, including multi-dim tensor slicing.
Fixes https://github.com/pytorch/pytorch/issues/43511
Fixes https://github.com/pytorch/pytorch/issues/43125
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44335
Reviewed By: suo, jamesr66a
Differential Revision: D23682213
Pulled By: gmagogsfm
fbshipit-source-id: f74fe25370e89fbfd2b3727d95ce4e1c4ba8dec4
