Optimzie Newtonsoft.Json lib by removing Xml, Schema support and making it AOT-friendly for AOT game builds

Source/Editor/CustomEditors/CustomEditor.cs

@@ -604,9 +604,7 @@ namespace FlaxEditor.CustomEditors
                         JsonSerializer.Deserialize(obj, text);
                     }
                 }
-#pragma warning disable 618
-                else if (Newtonsoft.Json.Schema.JsonSchema.Parse(text) == null)
-#pragma warning restore 618
+                else if (!text.StartsWith("{") || !text.EndsWith("}"))
                 {
                     return false;
                 }