go/types, types2: order dependent type checker crash on incomplete value of alias

This crashes at tip:

```
type A I

type I = interface {
	m() T
}

type T [unsafe.Sizeof(I(nil))]int
```

This does not:

```
type I = interface {
	m() T
}

type T [unsafe.Sizeof(I(nil))]int
```

Note: this is an ordering bug with aliases that does _not_ rely on type instantiation to trigger. I think the fix is _probably_ just to expand the `isComplete` check to also cover alias types.