Support nested updates of objects through realm.create via UpdateMode.All

[kraenhansen]

What, How & Why?

This PR implements an initial solution for applying the UpdateMode to all objects when passed to Realm.create().

This closes #5933.

☑️ ToDos

• 📝 Changelog entry
• 🚦 Tests

[kraenhansen]

While having a state (currentUpdateMode on Realm) might work for now, I'd suggest avoiding storing and maintaining state for operations as it has a couple of drawbacks:

• It can cause weird bugs if not properly set between calls of the operation.
  • If the reset happen at the end, it might not happen if an exception is throw.
  • If it happens in the beginning (as your suggestion is too), the deep dependent code has implicit dependencies on the state being sat before it's called, which isn't easily expressed in code and you'd need to rely on documentation. This makes the deep code less composable and therefore harder to reuse.
• It will make it more difficult to transition the implementation into asynchronous code (i.e. make it harder to change if we wanted to), since that might introduce concurrent calls into the deep code and it can't reasonably expect the state to originate from its particular invocation.

All in all, I'd suggest refactoring to passing the update mode through argument, possibly by adding a property to the CreationContext.

[elle-j]

@kraenhansen, very valuable input! We've discussed various issues and options on Slack (see our channel) with your input in mind. For now we've opted to move forward with the initial solution (but using try-finally for setting/unsetting currentUpdateMode), and creating a ticket for finding a more ideal solution for a later v12 release.

[takameyer]

Great! Just a few clarifying questions/suggestions