Add test for structured binding declaration hiding variable

Author: jketema

cpp/ql/test/query-tests/Best Practices/Hiding/DeclarationHidesVariable/DeclarationHidesVariable.expected

@@ -1,2 +1,4 @@
 | hiding.cpp:6:17:6:17 | i | Variable i hides another variable of the same name (on $@). | hiding.cpp:4:13:4:13 | i | line 4 |
 | hiding.cpp:18:15:18:15 | k | Variable k hides another variable of the same name (on $@). | hiding.cpp:15:11:15:11 | k | line 15 |
+| hiding.cpp:38:10:38:10 | (unnamed local variable) | Variable (unnamed local variable) hides another variable of the same name (on $@). | hiding.cpp:36:8:36:8 | (unnamed local variable) | line 36 |
+| hiding.cpp:39:10:39:10 | (unnamed local variable) | Variable (unnamed local variable) hides another variable of the same name (on $@). | hiding.cpp:36:8:36:8 | (unnamed local variable) | line 36 |

cpp/ql/test/query-tests/Best Practices/Hiding/DeclarationHidesVariable/hiding.cpp

@@ -30,3 +30,12 @@ void nestedRangeBasedFor() {
     for (auto y : ys) // GOOD
       x = y = 0;
 }
+
+void structuredBinding() {
+  int xs[1] = {1};
+  auto [x] = xs;
+  {
+    auto [x] = xs; // BAD
+    auto [y] = xs; // GOOD [FALSE POSITIVE]
+  }
+}