Introduce utility method SubscripitonManager.canManageSubscriptionAsUser

SubscriptionManager.canManageSubscription always uses the user context
created from SubscriptionManager to query packages. It is usually the
system user in phone process services. When the carrier app is installed
on secondary users (e.g. main user in HSUM) only, the query will fail.

The new utility method allows phone process components to query packages
as designed user and avoid duplicated logic in services side.

Bug: 371452139
Test: FrameworksTelephonyTests
Flag: com.android.internal.telephony.flags.hsum_package_manager
Change-Id: Icc1376744de356e2bb3dcf2e7bf68d89b97c16ad