[Sparse] Add reference implementation for addmv (#97353)
Partially addresses the problem raised in https://github.com/pytorch/pytorch/issues/96972
Add `test_addmv` and enable `test_block_addmv` on all platforms (so the test could be run on M1)
TODO: Make sure that test_block_addmv non-contiguous mode actually
generate non-contiguous as rigth now it probably does not, as test
passes assuming values are contiguous.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97353
Approved by: https://github.com/cpuhrsch
