[clang] [CIR] Implement PromotableRegionOpInterface for `cir.if` and `cir.scope` (PR #215780)

[Bruno Cardoso Lopes via cfe-commits]

https://github.com/bcardosolopes commented:

Nice! Few comments inline but mostly good. Might be nice to have an end-to-end tests as well (all the way from C/C++)

https://github.com/llvm/llvm-project/pull/215780