[clang][Sema] Fix false positive -Wshadow with structured binding captures (#157667)

Previously, lambda init captures of structured bindings were incorrectly
classified as regular shadow warnings (shown with `-Wshadow`), while
regular parameter captures were correctly classified as
`uncaptured-local` warnings (shown only with `-Wshadow-all`). This
created inconsistent behavior:

```cpp
  void foo1(std::pair<int, int> val) {
    [val = std::move(val)](){}();  // No warning with -Wshadow (correct)
  }

  void foo2(std::pair<int, int> val) {
    auto [a, b] = val;
    [a = std::move(a)](){}();      // Warning with -Wshadow (incorrect)
  }
```

The fix extends the existing lambda capture classification logic in
`CheckShadow()` to handle `BindingDecl` consistently with `VarDecl`,
ensuring both cases show no warnings with `-Wshadow` and
`uncaptured-local` warnings with `-Wshadow-all`.

Fixes #68605.

---------

Co-authored-by: Mariya Podchishchaeva <mariya.podchishchaeva@intel.com>