[mlir][sparse] Adding safe comparison functions to MLIRSparseTensorRuntime.

Different platforms use different signedness for `StridedMemRefType::sizes` and `std::vector::size_type`, and this has been causing a lot of portability issues re [-Wsign-compare] warnings.  These new functions ensure that we need never worry about those signedness warnings ever again.

Also merging CheckedMul.h into ArithmeticUtils.h

Reviewed By: aartbik

Differential Revision: https://reviews.llvm.org/D138149