Implement GetRegionCode and add the RegionCode to settings (#999)

This implement `GetRegionCode` accordingly to RE. I've added a setting in the GUI and a field in the Configuration file with a way to update the Configuration file if needed.

Ryujinx.HLE/HOS/Services/Settings/ISettingsServer.cs

@@ -54,6 +54,24 @@ namespace Ryujinx.HLE.HOS.Services.Settings
             return ResultCode.Success;
         }
 
+        [Command(4)]
+        // GetRegionCode() -> u32 nn::settings::RegionCode
+        public ResultCode GetRegionCode(ServiceCtx context)
+        {
+            // NOTE: Service mount 0x8000000000000050 savedata and read the region code here.
+
+            SystemRegion regionCode = (SystemRegion)context.Device.System.State.DesiredRegionCode;
+
+            if (regionCode < SystemRegion.Min || regionCode > SystemRegion.Max)
+            {
+                regionCode = SystemRegion.USA;
+            }
+
+            context.ResponseData.Write((uint)regionCode);
+
+            return ResultCode.Success;
+        }
+
         [Command(5)]
         // GetAvailableLanguageCodes2() -> (u32, buffer<nn::settings::LanguageCode, 6>)
         public ResultCode GetAvailableLanguageCodes2(ServiceCtx context)

Ryujinx.HLE/HOS/SystemState/SystemRegion.cs

@@ -0,0 +1,16 @@
+namespace Ryujinx.HLE.HOS.SystemState
+{
+    public enum SystemRegion
+    {
+        Japan,
+        USA,
+        Europe,
+        Australia,
+        China,
+        Korea,
+        Taiwan,
+
+        Min = Japan,
+        Max = Taiwan
+    }
+}

Ryujinx.HLE/HOS/SystemState/SystemStateMgr.cs

@@ -37,6 +37,8 @@ namespace Ryujinx.HLE.HOS.SystemState
 
         internal long DesiredLanguageCode { get; private set; }
 
+        internal uint DesiredRegionCode { get; private set; }
+
         public TitleLanguage DesiredTitleLanguage { get; private set; }
 
         internal string ActiveAudioOutput { get; private set; }
@@ -79,6 +81,11 @@ namespace Ryujinx.HLE.HOS.SystemState
             }
         }
 
+        public void SetRegion(SystemRegion region)
+        {
+            DesiredRegionCode = (uint)region;
+        }
+
         public void SetAudioOutputAsTv()
         {
             ActiveAudioOutput = AudioOutputs[0];