[clang] [clang][DebugInfo][test] Add tests for lambda capture packs (PR #160705)

[Yanzuo Liu via cfe-commits]

zwuis wrote:

I think this test case is needed: (by-reference, with initializer, and is a pack)

```cpp
return [&...params = args] {
  return /* ... */;
}();
```

https://github.com/llvm/llvm-project/pull/160705