Make getDefaultCarrierServicePackageName for Mainline

Make this API system to resolve mainline concern. It is ok to make it
system API as it is not a key in CarrierConfigManager. We can add
permission check on the other side.

Test: built
Bug: 146583148
Change-Id: I7c4297d659635622ba4523abf2ce32e21f961ad0
2 files changed