Add static zIndex example and e2e test to Catalyst (#42317)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/42317

Added a complicated zIndex test and corresponding screenshot test for it.

Changelog: [Internal]

Reviewed By: NickGerleman

Differential Revision: D52439963

fbshipit-source-id: 54bc8cfc9aa2e3c985279fe43027b3db88057c68