App history ordering/transition tests

These are meant to test the ordering between various events and promises, as well as in some cases how the navigation.transition values changes.

Some of them use the Recorder framework in resources/helpers.mjs, and others test tricky cases (e.g. reentrancy) in a more ad-hoc way.

https://github.com/WICG/app-history/#complete-event-sequence is a useful reference for the intent of these tests.

Note:

• Variants specifically exist for currententrychange because an event listener existing for currententrychange causes code to run, and thus microtasks to run, at a very specific point in the navigation-commit lifecycle. We want to test that it doesn't impact the ordering.
• Similarly we test that transitionWhile(Promise.resolve()) does not change the ordering compared to no transitionWhile() call, for same-document navigations, by trying to ensure most variants have appropriate transitionWhile() counterparts with similar orderings.

TODOs:

• Also test popstate and hashchange once https://github.com/whatwg/html/issues/1792 is fixed.