Close#31684.
In some rxjs operator, such as `retryWhen`, rxjs internally will set
`Subscription._unsubscribe` method to null, and the current zone.js monkey patch
didn't handle this case correctly, even rxjs set _unsubscribe to null, zone.js
still return a function by finding the prototype chain.
This PR fix this issue and the following test will pass.
```
const errorGenerator = () => {
return throwError(new Error('error emit'));
};
const genericRetryStrategy = (finalizer: () => void) => (attempts: Observable<any>) =>
attempts.pipe(
mergeMap((error, i) => {
const retryAttempt = i + 1;
if (retryAttempt > 3) {
return throwError(error);
}
return timer(retryAttempt * 1);
}),
finalize(() => finalizer()));
errorGenerator()
.pipe(
retryWhen(genericRetryStrategy(() => {
expect(log.length).toBe(3);
done();
})),
catchError(error => of(error)))
.subscribe()
```
PR Close#37091
JiaLiPassion