[clang] Reapply "[Clang] Improve diagnostics for expansion length mismatch" (PR #121044)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

(I plan to merge this after the branch 20 cut to avoid any potential revert churn. So it will stay in draft for now)

https://github.com/llvm/llvm-project/pull/121044