misc: move Models & Helpers into Common & Avalonia projects

src/Ryujinx/Common/Models/Github/GithubReleasesJsonSerializerContext.cs

@@ -0,0 +1,7 @@
+using System.Text.Json.Serialization;
+
+namespace Ryujinx.Ava.Common.Models.Github
+{
+    [JsonSerializable(typeof(GithubReleasesJsonResponse), GenerationMode = JsonSourceGenerationMode.Metadata)]
+    public partial class GithubReleasesJsonSerializerContext : JsonSerializerContext;
+}