Add notifications for the concurrent display mode

Show system notifications when the concurrent display mode is active
or when the concurrent display mode is canceled due to critical thermal
condition.

Summary of the changes:
1. Added DeviceStateNotificationController to manage the device state
   notifications.
2. In DeviceStateProvider, added "reason" to the callback
   onSupportedDeviceStatesChanged to indicate the cause of the supported
   device states change (e.g. change due to thermal condition)
3. In OverrideRequestController, added flags to the onStatusChanged
   callback to indicate the cause of status change (e.g.
   FLAG_THERMAL_CRITICAL means that the change is caused by critical
   thermal condition).
4. In OverrideRequest, added a uid field, which is used to get the app
   name displayed in the notification.

Fix: 266096470, 261127342, 264799106
Test: atest com.android.server.policy.DeviceStateProviderImplTest
com.android.server.devicestate.DeviceStateManagerServiceTest
com.android.server.devicestate.OverrideRequestControllerTest
com.android.server.devicestate.DeviceStateNotificationControllerTest

Change-Id: Ieb590d47dfbfd37e9e732b179a63ed25e080d0f0