Support sparse tensor output.

Add convertFromMLIRSparseTensor to the supporting C shared library to convert
SparseTensorStorage to COO-flavor format.

Add Python routine sparse_tensor_to_coo_tensor to convert sparse tensor storage
pointer to numpy values for COO-flavor format tensor.

Add a Python test for sparse tensor output.

Reviewed By: aartbik

Differential Revision: https://reviews.llvm.org/D115557