[mlir][sparse] replace specialized buffer setup with util code (#68461)

This completely centralizes all set up related to dim2lvl and lvl2dim
for the runtime library (and even parts of direct IR codegen) into one
place! And all comptatible with the MapRef data structure that should be
used in all remaining clients of dim2lvl and lvl2dim.

NOTE: the convert_x2y.mlir tests were becoming too overloaded
      so I decided to bring them back to the basics; if e.g.
      more coverage of the foreach is required, they should
      go into isolated smalle tests