Add a hidden API for Cross Profile Calendar Settings UI.

Settings wants to know if there is currently any package that is allowed
for cross profile calendar by PO.
The UI is added in work account settings, which actually runs
in primary user, and we can't call the public
getCrossProfileCalendarPakcages(work_user_admin) from primary user.
So we need to add this hidden API.

Bug: b/117976974
Test: make ROBOTEST_FILTER=CrossProfileCalendarPreferenceControllerTest -j40 RunSettingsRoboTests
Change-Id: I3df29a25a7826639828041b47dcfb7dcf086c411