The frame creation pass now considers scope of captured variable
introduction instead of closure creation, so the ordering can change if
two or more nested functions access variables 'outside-in', e.g.

```csharp
{
    int x = 0;
    {
        int y = 0;
        int L1() => y;

        {
             int z = 0;
             int L2() => x;
        }
    }
}
```

If we visit closures in-order in the previous example, we create frames
for L1, then L2. If we visit captured variables scopes, however, we
visit `x` (captured by L2), then `y` (captued by L1).