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: I74f9b04dc53bb6758a72e44d96959701f2b84634