Refactor the friend namespace (#721)

* Refactor the friend namespace and UInt128

This commit also:
- Fix GetFriendsList arguments ordering.
- Add GetFriendListIds.
- Expose the permission level of the port instance.
- InvalidUUID => InvalidArgument

* friend: add all cmds as commments

* add Friend structure layout

* Rename FriendErr to FriendError

* Accurately implement INotificationService

* Fix singleton lock of NotificationEventHandler

* Address comments

* Add comments for IDaemonSuspendSessionService cmds

* Explicitly define the Charset when needed

Also make "Nickname" a string

* Address gdk's comments

Ryujinx.HLE/HOS/Services/Friend/NotificationEventHandler.cs

@@ -0,0 +1,83 @@
+using Ryujinx.HLE.Utilities;
+
+namespace Ryujinx.HLE.HOS.Services.Friend
+{
+    public sealed class NotificationEventHandler
+    {
+        private static NotificationEventHandler instance;
+        private static object                   instanceLock = new object();
+
+        private INotificationService[] _registry;
+
+        public static NotificationEventHandler Instance
+        {
+            get
+            {
+                lock (instanceLock)
+                {
+                    if (instance == null)
+                    {
+                        instance = new NotificationEventHandler();
+                    }
+
+                    return instance;
+                }
+            }
+        }
+
+        NotificationEventHandler()
+        {
+            _registry = new INotificationService[0x20];
+        }
+
+        internal void RegisterNotificationService(INotificationService service)
+        {
+            // NOTE: in case there isn't space anymore in the registry array, Nintendo doesn't return any errors.
+            for (int i = 0; i < _registry.Length; i++)
+            {
+                if (_registry[i] == null)
+                {
+                    _registry[i] = service;
+                    break;
+                }
+            }
+        }
+
+        internal void UnregisterNotificationService(INotificationService service)
+        {
+            // NOTE: in case there isn't the entry in the registry array, Nintendo doesn't return any errors.
+            for (int i = 0; i < _registry.Length; i++)
+            {
+                if (_registry[i] == service)
+                {
+                    _registry[i] = null;
+                    break;
+                }
+            }
+        }
+
+        // TODO: Use this when we will have enough things to go online.
+        public void SignalFriendListUpdate(UInt128 targetId)
+        {
+            for (int i = 0; i < _registry.Length; i++)
+            {
+                if (_registry[i] != null)
+                {
+                    _registry[i].SignalFriendListUpdate(targetId);
+                }
+            }
+        }
+
+        // TODO: Use this when we will have enough things to go online.
+        public void SignalNewFriendRequest(UInt128 targetId)
+        {
+            for (int i = 0; i < _registry.Length; i++)
+            {
+                if (_registry[i] != null)
+                {
+                    _registry[i].SignalNewFriendRequest(targetId);
+                }
+            }
+        }
+    }
+}