Move NetworkScorerAppManager into com.android.server.

NetworkScorerAppManager is only used internally by the
NetworkScoreService and no longer needs to be part of core.
Extracted its inner class, NetworkScorerAppData, into a top-level
class and left it in android.net as it's used as part of the
NetworkScoreManager API.

Test: runtest frameworks-services -c com.android.server.NetworkScorerAppManagerTest
Test: runtest frameworks-services -c com.android.server.NetworkScoreServiceTest
Bug: 35095406
Change-Id: I201f081e05d0a909b4ae3142b63afc3e21548f77