[clang] [CIR] Initial upstreaming of idiom recognizer pass (PR #172486)

[Henrich Lauko via cfe-commits]

xlauko wrote:

In general, I don’t think this should be a single pass, or at least it should be configurable which idioms are raised.
It may not be desirable to raise everything every time.

https://github.com/llvm/llvm-project/pull/172486