[mlir][sparse] Improve ConcatenateOp rewriting for annotated all dense result.

[mlir][sparse] Improve ConcatenateOp rewriting for annotated all dense result.

Previously, we rely on InsertOp to add values to the result, in the same way we
add values to a sparse tensor with compressed dimensions. We now direct store
values to the values buffer.

Reviewed By: Peiming

Differential Revision: https://reviews.llvm.org/D141517