Updated namespace imports from AssetRipper.Processing to AssetRipper.Processing.Prefabs in multiple files. Changed list initialization syntax in GameObjectHierarchyObject.cs and SceneHierarchyObject.cs. Removed generic type specification from Where method call in PrefabProcessor.cs.
* Add PrefabHierarchyObject and SceneHierarchyObject
* Scene ordering remains the same, but prefabs get sorted by asset type
* This might solve an issue with pptr's inside a prefab. Previously, AssetsExportCollection.File was not changing while enumerating ExportableAssets.
* SceneExportCollection uses random export id's for artificially generated assets. Previously, there were no generated assets in scenes.