Handle managed profile with unified challenge in getHashFactor()

Settings passes null into getHashFactor() when a profile user has
unified challenge. In this case getHashFactor() needs to derive the real
profile password before it can calculate the hash factor.

Bug: 80077655
Test: runtest frameworks-services -c com.android.server.locksettings.SyntheticPasswordTests
Change-Id: Ifa1d88818b58f914fd3560bb6ef44012facde87b