Add new onUidProcAdjChanged callback to be consumed by the camera

service.

The camera service needs to know when individual process oom adj scores
are changed in order to address bug #124224342. When two separate
processes are displayed in split screen and focus is switched between
them, both proc states will remain the same while their oom scores
change. This is a problem if both have access to the camera - we want
only one owner of the camera stream at any given time and for the app
in focus to be the one to own it.

This patch adds a new IUidObserver registration level for individual
process oom score changes. In addition a new callback has been added to
IUidObserver to track these changes.

Change-Id: I68d964f474d20f819f54b614a4e314ce00aac8fb
Bug: 124224342
Test: -- ActivityManagerServiceTest
      -- ActivityManagerProcessStateTest
      -- ActivityManagerFgsBgStartTest
      -- UidObserverControllerTest
      -- NetworkPolicyManagerServiceTest
      -- ShortcutManagerTest2
      -- HintManagerServiceTest
      -- VibrationSettingsTest
      -- CameraEvictionTest#testCamera2AccessCallbackInSplitMode (x100)