A bug when destructuring in a for .. of loop

Minimal test case:

```js
{
let a;
}
for (const [a] of b) a();
```

Produces:

```js
{
var a;
}
for (var i = 0, list = b; i < list.length; i += 1) {
var ref = list[i];
var a = ref[0];

a$1();
}
```

Note that the `a$1` reference at the end is incorrect, since this symbol is not defined.

Start with the minimal JavaScript test case in the issue and trace the compiler handling for-of loops with destructuring and shadowed bindings. Add a regression test for this example and verify that the generated code references a defined symbol rather than the incorrect a$1 reference.

Written by the indexing model from the issue text.