Allowing activity occludes keyguard if activity has showWhenLocked flag

Manual testing steps:
- Add showWhenLocked flag to an activity in the manifest
- Start the activity from the managed profile when
  the device is locked
- Verify the activity is shown without having to
  enter the device or work challenge

Bug: 221389857
Test: com.android.server.am.ActivityManagerServiceTest
      Manual testing

Change-Id: I26a3c27b0f8afa3c4b00a35a788f0b2900dde932