Ensure TelecomServiceImpl uses System API when checking isSameApp.

To support eventual Telecom mainline modularization, this CL removes dependencies on hidden API UserHandle#isSameApp.

Bug: 382119556
Change-Id: Ibffdb2d5dcefc55b488b4bca86580d8319843dbf
Test: Manual + atest TelecomServiceImplTest
Flag: com.android.server.telecom.flags.allow_system_apps_resolve_voip_calls