Deprecate user pre-creation methods in UserManager.

Pre-created users are deprecated. This CL marks
UserManager#preCreateUser as deprecated and logs warning when invoked.
Also deprecate UserManager#getUsers(boolean, boolean, boolean).

Both are @TestApi methods, and will be removed once all callers are
migrated/removed.

Bug: 253528462

Test: atest com.android.server.pm.UserManagerTest

Change-Id: Ia6a2b1ae26303033a735b421475f93055bab8e8e