[LoopFusion] Sorting of undominated FusionCandidates crashes

This patch tries to fix [[ https://github.com/llvm/llvm-project/issues/56263 | issue ]].

If two **FusionCandidates** are in same level of dominator tree then, they will not be dominates each other. But they are control flow equivalent. To sort those FusionCandidates **nonStrictlyPostDominate** check is needed.

Reviewed By: Narutoworld

Differential Revision: https://reviews.llvm.org/D139993