If bound methods or fields are re-assigned, they become shared between instances

If bound methods or fields are re-assigned, they become shared between instances

Found this issue while trying to debounce bound method

Below test will fail

```
class A {
@boundMethod
bound() {}
}

const a = new A();
const b = new A();
a.bound = {
foo: 'bar'
};
assert.notEqual(a.bound, b.bound);
```