New API for getting the screen lock complexity

Return parent profile screen lock complexity if unified challenge is used

Bug: 111173457
Test: atest FrameworksCoreTests:PasswordMetricsTest
      atest FrameworksServicesTests:DevicePolicyManagerTest
      atest CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.PasswordComplexityTest
      manual test with sample app

Change-Id: I99f8bd644c5119590f49add98f216c4a527d6f2d