Android: Inter-process Data Observers

[greenrobot]

With version 2.7 came read-only stores, which is a great fit for using ObjectBox in a multi-process app. For details and an example see here: https://github.com/objectbox/objectbox-examples/tree/main/android-app-multiprocess

So, to make data observers work across we need some IPC (inter-process communication). I'd guess Android broadcasts would be sufficient to the task (e.g. no need for services etc.). Add the type IDs with changes to the broadcast, and that might already be the foundation for this.