[llvm] [MachineSink] Only add sink candidate if toBB is a successor of fromBB (PR #98540)

[Min-Yih Hsu via llvm-commits]

https://github.com/mshockwave commented:

Could you add this check into `isLegalToBreakCriticalEdge` since any pair of `FromBB` & `ToBB` can subject to this issue, not just the deferred one?

Also, please add tests.

https://github.com/llvm/llvm-project/pull/98540