[tests] add more portal activity tests (facebook#35095)

I copied some tests from
[`Activity-test.js`](https://github.com/facebook/react/blob/1d68bce19c9409ed70604d1d16b70b68ce71dc4a/packages/react-reconciler/src/__tests__/Activity-test.js)
and made them portal specific just to confirm my understanding of how
Portals + Activity interact is correct. Seems good to include them.

Author: rickhanlonii