[clang] [clang] Add test for CWG2149 "Brace elision and array length deduction" (PR #90079)

[via cfe-commits]

cor3ntin wrote:

Can you add examples 14, 16, 17, 18 of the paper?
I'd be if they are only tested in C++11+ modes
Then we can mark the paper as implemented (bonus point for finding the oldest conforming version)

https://github.com/llvm/llvm-project/pull/90079