Add Identity Check Test API

The API is BiometricManager#setIsIdentityCheckActive(IdentityCheckStatus)
and is hidden. It is for testing purpose ONLY.

Flag: android.hardware.biometrics.identity_check_test_api
Test: atest BiometricSimpleTests
Bug: 347123256

Change-Id: I5f5d321656116c47fa0ae820029cfa3d31ddb62a