Begin watching mIsolatedOwners

This change swaps the type for mIsolatedOwners in PackageManagerService and the
Computer from a SparseIntArray to a WatchedSparseIntArray to ensure that
changes to it are propogated to the snapshotting system.

Bug: 180418767
Change-Id: Ifa0890d07398adc727884ef0e15dd86843c5146f