Fix usages of PackageManager APIs in Telephony

Remove usages of the hidden PackageManager#*asUser methods from
Telephony, and add some unit tests to verify the functionality.

Test: atest FrameworksTelephonyTests
Test: atest TelephonyCommonTests
Bug: 146834818
Change-Id: Ifc32ee29c488193c49070db11555899a93ceec0d