Consolidate UserID+Package classes.

https://xkcd.com/927/

Many different components have created their own classes to represent a
userID+packageName combination. This means 1) duplicate code, 2)
duplicate objects in memory representing the same thing. Creating a
common class that limits itself to one object per userID+packageName
combo addresses those two concerns.

There are still others with similar classes. They're not included in
this CL because they have slight differences and would require a little
bit more work to consolidate.

Bug: 141645789
Bug: 247127880
Test: atest CtsAccountManagerTestCases
Test: atest CtsContentTestCases:OverlayManagerTest
Test: atest CtsShortcutManagerTestCases
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/tare
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/om
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/pm
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/tare
Test: atest FrameworksMockingServicesTests:PrefetchControllerTest
Test: atest FrameworksMockingServicesTests:QuotaControllerTest
Change-Id: I63d5bc946cc7b24a0536e8b2051da07a801b3a8a