[mlir][sparse] introduce vectorization pass for sparse loops

[mlir][sparse] introduce vectorization pass for sparse loops

This brings back previous SIMD functionality, but in a separate pass.
The idea is to improve this new pass incrementally, going beyond for-loops
to while-loops for co-iteration as welll (masking), while introducing new
abstractions to make the lowering more progressive. The separation of
sparsification and vectorization is a very good first step on this journey.

Also brings back ArmSVE support

Still to be fine-tuned:
  + use of "index" in SIMD loop (viz. a[i] = i)
  + check that all ops really have SIMD support
  + check all forms of reductions
  + chain reduction SIMD values

Reviewed By: dcaballe

Differential Revision: https://reviews.llvm.org/D138236