[SimplifyCFG] `FoldBranchToCommonDest()`: allow branch-on-select

This whole check is bogus, it's some kind of a profitability check.
For now, simply extend it to not only allow branch-on-binary-ops,
but also on poison-safe logic ops.

Refs. https://github.com/llvm/llvm-project/issues/53861
Refs. https://github.com/llvm/llvm-project/issues/54553