nfp:user: Implement IUser (#714)

* nfp:user: Implement IUser

- Based on RE of sysmod FW 1.0 and 3.0 with help of https://github.com/switchbrew/libnx/ and https://reswitched.github.io/SwIPC/ifaces.html#nn::nfp::detail::IUser
- Accurate implementation of Initialize, AttachActivateEvent, AttachDeactivateEvent, GetState, GetDeviceState, GetNpadId and GetDeviceState.
- Implementation of Finalize and ListDevices (close #638).

* reorder private var

* fix nits

Ryujinx.HLE/HOS/Services/Nfc/Nfp/IUserManager.cs

@@ -0,0 +1,27 @@
+using Ryujinx.HLE.HOS.Ipc;
+using System.Collections.Generic;
+
+namespace Ryujinx.HLE.HOS.Services.Nfc.Nfp
+{
+    class IUserManager : IpcService
+    {
+        private Dictionary<int, ServiceProcessRequest> _commands;
+
+        public override IReadOnlyDictionary<int, ServiceProcessRequest> Commands => _commands;
+
+        public IUserManager()
+        {
+            _commands = new Dictionary<int, ServiceProcessRequest>
+            {
+                { 0, GetUserInterface }
+            };
+        }
+
+        public long GetUserInterface(ServiceCtx context)
+        {
+            MakeObject(context, new IUser());
+
+            return 0;
+        }
+    }
+}