Ensure AppLabelProxy is multiuser aware.

This CL ensures that AppLabelProxy is multiuser aware by removing the dependency on a singular passed in package manager. Instead the correctly associated userHandle is passed in and the correct context is derived from that. Then the correct package manager is derived from that context.

Bug: 321817633
Flag: com.android.server.telecom.flags.telecom_app_label_proxy_hsum_aware
Test: PhoneAccountRegistrarTest + CallScreeningServiceFilterTest
Change-Id: I610efe388c6ad5d98f57770d22c0b5a0fd717a4b