message: test(dtslint): add infer tests to distinctUntilKeyChanged
diff: @@ -3,6 +3,14 @@ import { distinctUntilKeyChanged } from 'rxjs/operators';
  const sample = {name: 'foobar', num: 42};
  +it('should infer correctly', () => {
  + const o = of(sample).pipe(distinctUntilKeyChanged('name')); // $ExpectType Observable<{ name: string; num: number; }>
  +});
  +
  +it('should infer correctly with compare', () => {
  + const o = of(sample).pipe(distinctUntilKeyChanged('name', () => true)); // $ExpectType Observable<{ name: string; num: number; }>
  +});
  +
  it('should enforce key set', () => {
  const o = of(sample).pipe(distinctUntilKeyChanged('something')); // $ExpectError
  });
  