Support Coroutines in Espresso

With the [deprecation of `AsyncTask`](https://android-review.googlesource.com/c/platform/frameworks/base/+/1156409/6/core/java/android/os/AsyncTask.java#196) I'd imagine many apps are starting to look at a switch to coroutines. One outstanding problem is that (as far as I'm aware) Espresso does not have the same support for coroutines as it does for `AsyncTask` - as the [docs say](https://developer.android.com/training/testing/espresso/) Espresso will not make assertions until "There are no instances of AsyncTask currently executing a task".

This feature has always been a massive positive for Espresso and makes TDD/BDD workflows in Android comparatively easy so the lack of coroutine support is still a large blocker for adopting them - for me at least.

Start by reviewing Espresso's existing AsyncTask synchronization behavior and the linked Espresso documentation. The work is done when Espresso provides equivalent synchronization for coroutines so assertions wait until relevant coroutine work has completed.

Written by the indexing model from the issue text.