Espresso Has No Way To Assert Root Doesn't Exist

There seems to be no good way to assert that a PopupWindow is **not** visible.

Basically, this:

https://stackoverflow.com/questions/54116938/how-to-check-that-popup-notification-is-not-displayed-espresso

This works but has a 60 sec timeout before the exception is thrown so it's no good.
```
assertThrows(
NoMatchingRootException.class,
() -> onView(isRoot()).inRoot(isPlatformPopup()).check(doesNotExist()));
```

The recommended solution works (use UiAutomator) but shouldn't Espresso also have a way to do this?

Start by tracing Espresso's existing root matching and doesNotExist assertion behavior using the example in the issue. Compare it with the linked UiAutomator workaround and determine how a non-visible PopupWindow should be asserted without the 60-second timeout. Done means Espresso provides a reliable assertion for this case.

Written by the indexing model from the issue text.