[clang] [clang] Represent array refs as `TemplateArgument::Declaration` (PR #80050)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I don't have concerns as written.  @cor3ntin : feel free to accept if you like it too.

https://github.com/llvm/llvm-project/pull/80050