Fixing MainThreadInitializedObject

> Making SafeCloseable implementation mandatory, to prevent leaks during test and preview
> Removing getNoCreate method and defining executeIfCreated to avoid null pointer exceptions
> Fixing sandbox value leaking into main, by Checking sandbox against App context
> Converting sanbox to an interface instead a class

Bug: 335280439
Test: Presubmit
Flag: None
Change-Id: I951dcde871898e745ff6490a1c4f8fd1512888f5