[clang] [Clang][diagnostics] Fix structured binding shadows template param loc (PR #129116)

[Erich Keane via cfe-commits]

================
@@ -162,3 +162,10 @@ struct A {
 };
 A<0>::B a;
 }
+
+template <typename T> void shadow() {  // expected-note{{template parameter is declared here}}
+  using arr = int[1]; // expected-warning at +1 {{decomposition declarations are a C++17 extension}}
----------------
erichkeane wrote:

```suggestion
  using arr = int[1];
   // expected-warning at +1 {{decomposition declarations are a C++17 extension}}
```

https://github.com/llvm/llvm-project/pull/129116