XamarinWithUnityApp

A Xamarin.Android app with Unity as a lib (a new feature in Unity 2019.3.a2, see this blog post and these steps).
So you can now easily add a Unity scene (e.g. ARCore scene) to any native or Xamarin app via .aar file.

Size (armv7a)

Unity stuff (*.aar): 16.2Mb
Xamarin stuff (including a few Android Support libs): 8Mb
Total APK size: 24.2Mb (IL Link + proGuard)