[clang] [Clang] [C++26] Implement P1306R5 Expansion Statements (PR #165195)

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin commented:

Thanks for working on this.
I started to review but I had barely any time to scratch the surface

https://github.com/llvm/llvm-project/pull/165195