Use real `PackageDataSnapshot`.

Also:
- Remove `sdk_version: "system_server_current"` from `ArtServiceTests`
  because `android_test` has no access to system server classes at
  runtime.
- Add "services.core" as `static_libs` instead.

Bug: 177273468
Test: adb shell pm art get-optimization-status com.google.android.youtube
Test: (on master-art) art/tools/buildbot-build.sh
Ignore-AOSP-First: ART Services
Change-Id: I0ca759bc04498a963cab540b6e0b93990712aca2