Resolve the true entry point during tests (#21505)

* Resolve the entry point for tests the same way builds do

This way the source tests, test the same entry point configuration.

* Gate test selectors on www

These are currently only exposed in www builds

* Gate createEventHandle / useFocus on www

These are enabled in both www variants but not OSS experimental.

* Temporarily disable www-modern entry point

Use the main one that has all the exports until we fix more tests.

* Remove enableCache override that's no longer correct

* Open gates for www

These used to not be covered because they used Cache which wasn't exposed.