[mlir][sparse] sparse storage scheme type conversion

This builds a compound type for the buffers required for the sparse storage scheme defined by the MLIR sparse tensor types. The use of a tuple allows for a simple 1:1 type conversion. A subsequent pass can expand this tuple into its component with an isolated 1:N type conversion.

Reviewed By: Peiming

Differential Revision: https://reviews.llvm.org/D133050