CPlusPlus: Support structured bindings

While we do recommend clangd for modern code bases, we should still be
able to parse basic language constructs.

Fixes: QTCREATORBUG-27975
Change-Id: I189b991685a5cd5f62f2afce77878b60c895e8f9
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: hjk <hjk@qt.io>

src/libs/3rdparty/cplusplus/ASTPatternBuilder.h

@@ -339,6 +339,13 @@ public:
         return ast;
     }
 
+    DecompositionDeclaratorAST *DecompositionDeclarator(NameListAST *names = nullptr)
+    {
+        const auto ast = new (&pool) DecompositionDeclaratorAST;
+        ast->identifiers = names;
+        return ast;
+    }
+
     NestedDeclaratorAST *NestedDeclarator(DeclaratorAST *declarator = nullptr)
     {
         NestedDeclaratorAST *ast = new (&pool) NestedDeclaratorAST;