[clang] [CIR] Upstream SelectOp and ShiftOp (PR #133405)

[Bruno Cardoso Lopes via cfe-commits]

https://github.com/bcardosolopes requested changes to this pull request.

Looks reasonable to add vector support later for shifts. Because `SelectOp` is independent of `ShiftOp`, one possibility would have been to split it in two PRs to land them faster, but wouldn't bother changing for this round.

https://github.com/llvm/llvm-project/pull/133405