[localization-editor] Error handling child prefab's Label

[smallmain]

If prefab A has a nested prefab B, and there is a Label in prefab B, sometimes the correct way is to override and add the l10nLabel component to prefab A, and sometimes to add the l10nLabel component directly to prefab B.

It depends on whether the user has Prefab B as a public component or as a separate component.

I think this can be identified by telling whether the string property has been modified.

But that might not be enough, maybe a way to mark certain Labels as public components is also needed.