AccountManagerService send pkg uid when creating notification channel

AccountManager needs to pass the app's uid explicitly in order for the
channel lookup to not fail. Requires separate API that only system can
call.

Bug: 36511867
Test: Install Clankium and reboot device, observe Notification
Change-Id: I6ddd87d755b4b2129565dd275e799b0349a80936
(cherry picked from commit 3560f847fbffa54f7841320cc0f722778df1222a)
5 files changed