SpatialTracking was part of core Unity Engine in 2018 version but has moved to assembly definition in 2019. This makes our SDK incompatible between those Unity versions. We have our own assembly definition in our Unity package which now has to link against UnityEngine.SpatialTracking in Unity 2019. What is the best way here to keep compatibility between 2018.3.x and all new 2019 Unity versions? So we do not have to release 2 independent packages for 2018 and 2019 versions. Thank you.