ActivityScenarioRule launches an EmptyActivity in between each test

This adds several hundred ms to each test using the Rule.

The separate launch should be confined to only the affected API levels:

https://github.com/android/android-test/blob/ef59895f4132aa13f01b263e5342d5cbb73b37a9/core/java/androidx/test/core/app/InstrumentationActivityInvoker.java#L469

Additionally, consider disabling animations with `overridePendingTransitions(0,0)` for EmptyActivity and similar, since most tests run with window animations enabled (and they're difficult to disable in Studio: https://issuetracker.google.com/issues/138120842)