Fix user starts by using startProfile

We used ActivityManager.startUserInBackground earlier to start the clone
user. As per the changes done recently (b/267800984),
UserVisibilityMediator now marks all the profiles/users started usign
startUserInBackground as startedInvisible. This results in the apps not
being able to launch on clone profile without a device restart. To fix
this, in this change we move to using ActivityManager.startProfile to
start the clone-user.

Test: Tested on device by creating clone profile through settings app
Bug: 268011720
Change-Id: I4a594cd4d10cfbd7459b04baa45719885decf87e