[mlir][sparse][NFC] Switch InitOp to bufferization::AllocTensorOp

[springerm]

Summary

Now that we have an AllocTensorOp (previously InitTensorOp) in the bufferization dialect, the InitOp in the sparse dialect is no longer needed.

Depends On D126179

[aartbik]

I really like the direction this is going in, so we have one centralized mechanism to reason on allocation (and deallocation) of the buffers for tensors!
In the long run, it would be nice to have bufferization.de_alloc_tensor() as well, and have one mechanism that inserts those, independent of dense/sparse tensors.

mlir/include/mlir/Dialect/SparseTensor/IR/SparseTensorOps.td

57–60

can we move some of this explanation and the example into the doc of bufferization.alloc_tensor?

[springerm]

update

[springerm]

fix test

[springerm]

typo

[aartbik]

I really like the unification, since the original separation felt artificial!

Once this goes in, you will probably give a heads up to some of the other projects that depend on this, but outside this source tree.

mlir/include/mlir/Dialect/Bufferization/IR/BufferizationOps.td

37

This comment ("helper") feels a bit too strong. Right now, it is the only way to materialize a tensor into a computation. Can we just say something like, the reason for this op is ....., (something like that)