Allow privileged carrier app to update subscription nickname.

Make EuiccManager#updateSubscriptionNickname as public API to allow
carrier app to call it.
Only a privileged app of the given subscription can update the
subscription nickname.
Refresh cached subscription list after the nickname is successfully
updated.

Bug: 122597547
Test: test on phone
Change-Id: I63c5ec4366f32735a54adf40b9cc0b47af681736