Add necessary system APIs for moving role into module.

- Added Context.getUser() to system API, to allow module framework
classes to also implement multi-user support in manager classes.

- Added PackageManager.getPermissionControllerPackageName() to system
API for RoleControllerManager to know which package to bind to.

Bug: 158736025
Test: build
Change-Id: If69a97573eb1e676145e0accdfa73fef320aabe7