Add isManagedKiosk system APIs.

Add system APIs isManagedKiosk and isUnattendedManagedKiosk. These will
be defined in the CDD.

The intention is to have privacy and security-approved definitions that
future features (removing user consent dialogs, stronger APIs) can use
specifically for publicly-accessible dedicated devices.

We use 'kiosk' rather than 'publicly-accessible dedicated device' for
ease-of-use, which is actually consistent with ChromeOS.

Bug: 111384878
Test: Each use will have its own CTS tests. The definitions themselves
will be in CDD. Currently tested by calling the methods in TestDPC.
Change-Id: If080a3b9dae285bc28823e6004750908009130d2