[SR] Add a copy variant for fused_split_and_squeeze
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75660
The outputs of `split_and_squeeze` are passed to `VarStack` in models we care about. `VarStack` has a [fast path](https://www.internalfb.com/code/fbsource/[893193f5277184fd17f4ea3f28fe415a4df37707]/fbcode/caffe2/aten/src/ATen/native/TensorShape.cpp?lines=296-298) for when all of its inputs have the same strides.
Hitting the slow path adds a ton of extra overhead - so much that it's worth it to copy in `split_and_squeeze` and force all of `VarStack`'s inputs to be contiguous so we can take advantage of the fast path.
Differential Revision: [D35513777](https://our.internmc.facebook.com/intern/diff/D35513777/)
**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D35513777/)!
Approved by: https://github.com/hlu1
