FIX: Device disconnected events are missed when running in the background (#1609)

Author: andrew-oc

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -16,6 +16,7 @@ however, it has to be formatted properly to pass verification tests.
 
 ### Fixed
 - Fixed composite bindings incorrectly getting a control scheme assigned when pasting into input asset editor with a control scheme selected.
+- Fixed an issue on PS5 where device disconnected events that happen while the app is in the background are missed causing orphaned devices to hang around forever and exceptions when the same device is added again ([case UUM-7842](https://issuetracker.unity3d.com/product/unity/issues/guid/UUM-6744)).
 
 ### Actions
 - Extended input action code generator (`InputActionCodeGenerator.cs`) to support optional registration and unregistration of callbacks for multiple callback instances via `AddCallbacks(...)` and `RemoveCallbacks(...)` part of the generated code. Contribution by [Ramobo](https://github.com/Ramobo) in [#889](https://github.com/Unity-Technologies/InputSystem/pull/889).

Packages/com.unity.inputsystem/InputSystem/NativeInputRuntime.cs

@@ -227,7 +227,11 @@ public float pollingFrequency
         public double currentTimeOffsetToRealtimeSinceStartup => NativeInputSystem.currentTimeOffsetToRealtimeSinceStartup;
         public float unscaledGameTime => Time.unscaledTime;
 
-        public bool runInBackground => Application.runInBackground;
+        public bool runInBackground => Application.runInBackground ||
+        // certain platforms ignore the runInBackground flag and always run. Make sure we're
+        // not running on one of those.
+        // TODO: Add more platforms here as they're discovered.
+        Application.platform == RuntimePlatform.PS5;
 
         private Action m_ShutdownMethod;
         private InputUpdateDelegate m_OnUpdate;