[mlir][sparse] introduce a new compressed(hi) dimension level type

`compressed(hi)` is similar to `compressed`, but instead of reusing the previous position high as the current position low, it uses a pair of positions for each sparse index.

The patch only introduces the definition (syntax) but does not provide codegen implementation.

Reviewed By: aartbik

Differential Revision: https://reviews.llvm.org/D148664