[clang] [clang] Lower _BitInt(129+) to a different type in LLVM IR (PR #91364)

[Mariya Podchishchaeva via cfe-commits]

Fznamznon wrote:

Well, I hope I got the idea right, I updated PR so now it is introducing `convertTypeForLoadStore` API, returning `iBITS` (Let `BYTES := sizeof(_BitInt(N))`, and let `BITS := BYTES * 8`).
I've also tried to inspect as many places where `ConvertTypeForMem`, `emitToMemory`, emitFromMemory` are used and actually found a couple of places that original patch broke.

https://github.com/llvm/llvm-project/pull/91364