Check cross user permissions for a given UID

Instead of relying on Context#checkCallingOrSelfPermission, explicitly
check permissions against a given UID. However, to maintain legacy
behavior, replace custom UIDs with Binder.getCallingUid when enforcing
permissions from a method.

Also update tests afftected by this change - by adding methods to mocked
objects

Additionally,
This reverts commit 7d0da763a044094c3a8fc51c28f3a0d9db8f9e3d.
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:6775f07552f15f6e4b934bb9552f7a6abff8060b)
Merged-In: Ib31cabff5714500471bd397c743e127c85751a5c
Change-Id: Ib31cabff5714500471bd397c743e127c85751a5c