Setting up input data for benchmarks and integration tests can be tedious in pure MLIR. With more sparse tensor work planned, this convenience library simplifies reading sparse matrices in the popular Matrix Market Exchange Format (see https://math.nist.gov/MatrixMarket). Note that this library is *not* part of core MLIR. It is merely intended as a convenience library for benchmarking and integration testing. Reviewed By: penpornk Differential Revision: https://reviews.llvm.org/D88856