Implement System Authority EnforcingAdmin.

Added new hidden API for system services to set/clear user resrictions
on a specified target user. This will be used for Automotive passenger
users (visible background users) in multi-user multi-display
configurations.

Bug: 324899199
Flag: EXEMPT hidden API
Test: atest FrameworksServicesTests:com.android.server.devicepolicy.DevicePolicyManagerTest
Test: manual test using MD emulator.
      visually check in Car Settings.
      $ adb shell dumpsys user
      $ adb shell dumpsys device_policy

Change-Id: I8993417786cfe4b608b49150cda73b3cb77908ea