Improvements on UserManagerService.

- Uses ActivityManagerInternal to get current user id.
- Removed permission checks from
  isCurrentUserOrRunningProfileOfCurrentUser().
- Added unit tests for these 2 methods.

Test: atest FrameworksMockingServicesTests:com.android.server.pm.UserManagerServiceTest
Test: atest CtsMultiUserTestCases:android.multiuser.cts.UserManagerTest

Bug: 244452695
Fixes: 244765233

Change-Id: Icc13b315f138235152cc2aca988dfe38ca914c67