[mlir][SparseTensor] Split scf.for loop into masked/unmasked parts

[mlir][SparseTensor] Split scf.for loop into masked/unmasked parts

Apply the "for loop peeling" pattern from SCF dialect transforms. This pattern splits scf.for loops into full and partial iterations. In the full iteration, all masked loads/stores are canonicalized to unmasked loads/stores.

Differential Revision: https://reviews.llvm.org/D107733