Add isSameApp to PackageManagerInternal

Adds a new method to PackageManagerInternal that checks
if a given package belongs to the calling uid. This logic also
accounts for calling uids in the sdk sandbox range.
Deduplicates two methods in NotificationManager and ActivityTaskManager
which have implemented this logic.

Bug: 219750831
Test: atest NotificationManagerServiceTest
Test: Manual test using Sdk Sandbox test app
Change-Id: I1c566f75c81112dfeeb664827dcb27768959c377