Improve testing (likely via CI) to try to ensure compatibility with specific Android SDKs

[cowtowncoder]

We have not been very successful in either determining or maintaining compatibility with Android SDKs, as witnessed by #3658.
It would be good to add compatibility testing somehow (same would of course be useful for JDK baseline as well, although for the moment we compile with same JDK as the baseline, Java 8).

Possibly useful links:

• Example of Android sub-project for testing compatibility: https://github.com/square/retrofit/tree/master/retrofit/android-test
• AnimalSniffer signatures for Android SDKs: https://github.com/open-toast/gummy-bears