create static method
Create an instance of ObjectBox to use throughout the app.
Implementation
static Future<ObjectBox> create() async {
final docsDir = await getApplicationDocumentsDirectory();
// Future<Store> openStore() {...} is defined in the generated objectbox.g.dart
final store = await openStore(directory: p.join(docsDir.path, "obx-example"));
return ObjectBox._create(store);
}