Removed HttpServer.

Re-implemented everything using ASP.NET.
Changed some requests to use JSON instead of FORM data.
Some work towards deleting the FIXMEGlobal instance.
Auth is missing, XSRF does not work correctly.

Duplicati/WebserverCore/Exceptions/UserReportedHttpException.cs

@@ -0,0 +1,9 @@
+namespace Duplicati.WebserverCore.Exceptions
+{
+    public abstract class UserReportedHttpException(string? Message = null)
+        : Exception(Message ?? "Error")
+    {
+        public abstract int StatusCode { get; }
+        public virtual string ContentType => "application/json";
+    }
+}