[mlir][sparse] implement singleton dimension level type

This is a first step towards fully implementing the new dimension
level types and properties, illustrating with a fully functional
sorted COO of any dimension. Note that the sparsification part is
pretty complete. The required parts in the runtime support library
have been kept to a minimum, to avoid huge conflicts with Wren's
ongoing refactoring. The missing parts will be filled in later.

Reviewed By: Peiming

Differential Revision: https://reviews.llvm.org/D134096