2D Strided to/from CSC, COO to CSC, CSC to CSC conversion. (#77521)
Adds
- to_sparse_csc for strided input
- to_sparse_csc for COO input
- CSC to strided
- CSC to CSR
- CSC to CSC
Uses SciPy as a reference
Follow up work is changing transpose to return CSC when passed CSR and the resulting ripples through our matmul operations.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77521
Approved by: https://github.com/pearu, https://github.com/anjali411
