Inherited accessors break when base is type-erased

When extending type-erased bases with accessors, the accessors are called with incorrect `this`. 

## Example

```typescript
const A = class {
    get value(): this {
        return this;
    }
} as any;

class B extends A {
    
}

const b = new B();
console.assert(b.value === b); // boom
```
