Calling `setAnonymousTracking` from non-main thread results in an `IllegalStateException` crash on Android 8

I have some code that listens for data changes within a flow in a coroutine on the `IO` dispatcher.
When the flow emits something, I call `setAnonymousTracking()` based on this data, which ends up calling `userReport.setAnonymousTracking(enabled)` in the end.

It turns out that this call has to be made from the main thread, otherwise I get an `IllegalStateException` with the message:
> Fatal Exception: java.lang.IllegalStateException
> Calling View methods on another thread than the UI thread.

Stack traceback after calling the API function:

```
com.android.webview.chromium.WebViewChromium.a (chromium-Monochrome.aab-stable-720417920:12)
android.webkit.WebView. (WebView.java:548)
com.audienceproject.userreport.InAppEventsTrack.getUserAgentString (InAppEventsTrack.java:227)
com.audienceproject.userreport.InAppEventsTrack. (InAppEventsTrack.java:65)
com.audienceproject.userreport.UserReport.initTracker (UserReport.java:130)
com.audienceproject.userreport.UserReport.init (UserReport.java:94)
com.audienceproject.userreport.UserReport. (UserReport.java:56)
com.audienceproject.userreport.UserReport.configure (UserReport.java:67)
com.audienceproject.userreport.UserReport.configure (UserReport.java:85)
```

There is no mention in the documentation that this needs to be called from the main thread. I also don't currently have an explanation for why only Android 8 has the crashes.

To fix it, I wrapped the call in `withContext(Dispatchers.Main)`.

This is where the WebView is created by the SDK and ends up crashing on Android 8:

```
private String getUserAgentString(Context context) {
try {
return new WebView(context).getSettings().getUserAgentString();
} catch (Exception ex) {
return null; // exception might appear if there is no google APIs
}
}
```

Start with InAppEventsTrack.getUserAgentString, where the payload shows a WebView is created, and trace the call through UserReport.initTracker, UserReport.init, and UserReport.configure. Reproduce setAnonymousTracking from a non-main thread on Android 8, then verify that the SDK no longer crashes while preserving the existing tracking behavior.

Written by the indexing model from the issue text.