[clang] [CIR] Lower builtin_launder (PR #197252)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

No concerns with the direction of moving things into `QualType` for better code sharing, but I did have some questions about moved code that may point out missed test coverage or bugs (don't have to solve any of it as part of this PR; perfectly fine to file issues for follow-up work).

https://github.com/llvm/llvm-project/pull/197252