AssetRegistry: In a packaged game ScanPathsSynchronous with bForceRescan=true will permanently forget about assets inside IOStore containers

This came up from several discussions on UDN and internal discussion.

The root cause is that the AssetRegistry currently cannot discover packages inside IOStore containers, it relies on the serialized AssetRegistry.bin to discover them.

In a packaged game, when calling ScanPathsSynchronous on a path with ForceRescan any known assets in the scanned path will be dropped before scanning.

The inability to scan for assets in IOStore containers will lead to the assets being deleted from the AR state and never re-added.

1. Load a game with IOStore assets.
2. Call ScanPathsSynchronous("/Game", bForceRescan=true)
3. Notice that any assets loaded from a serialized AssetRegistry.bin that are part of an IOStore container are now missing from the ARState