Warning "Entity has no registered owning instance" for nested prefabs in Asset Processor

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Warning "Entity has no registered owning instance" for nested prefabs in Asset Processor

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Some observations:

1. In this case, the prefab being processed is SuperCat. The owning instance is Cat and the entity is its (i.e. Cat) container entity.
2. If you remove CatEntity, the warning still persist, which means it is the container entity. If you duplicate Cat prefabs, there would be two warnings.
3. It only happens to nested prefabs.
4. Code that generates the warning: Prefabs/InstanceEntityIdMapper.cpp

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Note that the same warning also applies when we run the game in Editor. Related GHI: #14323

I believe it is the same root cause that happens when a prefab source asset is being converted to a product asset (spawnable).

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I added some log lines in the PrefabBuilder, PrefabCatchmentProcessor, InstanceSerializer, JsonEntityIdSerializer, and InstanceEntityIdMapper.

Based on the result, I can tell that the it is somehow unexpectedly checking whether a parent container entity (SuperCat) belongs to a nested instance (Cat). Specifically, when the serializer is processing the SuperCat prefab, it would process the container entity and its nested instance Cat prefab. It is good there. But when it is processing the Cat instance's container entity, it does this:

1. Checks if Cat container entity belongs to Cat instance - CORRECT (no issue)
2. Checks if SuperCat container entity belongs to Cat instance - WRONG

Don't know why the second ResolveReferenceId is being called for the SuperCat container entity. The serialization code is very hard to debug... I think there is a bug here.

Any ideas? @srikappa-amzn @michabr @AMZN-daimini