Update Fantom tests to use scrollTo (#50912)

Summary:
Pull Request resolved: #50912

Changelog: [Internal] - Update IntersectionObserver Fantom tests to use the new `scrollTo` api which didn't exist when I first wrote these tests. As well, do clean up between tests

Reviewed By: rubennorte

Differential Revision: D73551695

fbshipit-source-id: 9625328879230d178f23a089436f2a3c7b8323bd

Author: lunaleaps