[NNC] Add a non functional Tensor kind (#48750)
Summary:
Adds the CompoundTensor, a specialisation of the NNC Tensor which allows arbitrary production statements. This will allow lowering of aten ops into specific NNC IR patterns (which don't need to be functional) - allowing us to shortcut to the optimized form of common patterns.
This is part 1 of trying to clean up the lowering of aten::cat so it is easier to optimize.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48750
Reviewed By: tugsbayasgalan
Differential Revision: D25433517
Pulled By: nickgg
fbshipit-source-id: de13c4719f8f87619ab254e5f324f13b5be1c9da
