[clang] [clang] Emit -Wdangling diagnoses for cases where a gsl-pointer is construct from a gsl-owner object in a container. (PR #104556)

[Haojian Wu via cfe-commits]

hokein wrote:

Testing it a bit more, unfortunately, it has a false positive on the following case:

```
const char* kk() {
    std::optional<string_view> k;
    return k.value().data(); // dangling warning, but we should not diagnose it.
}
```

https://github.com/llvm/llvm-project/pull/104556