Introduce new OpenRA.exe entrypoint and change OpenRA.Game to a library.

OpenRA.Launcher/Program.cs

@@ -0,0 +1,39 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2020 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System;
+using System.Diagnostics;
+using System.Linq;
+
+namespace OpenRA.Launcher
+{
+	static class Program
+	{
+		[STAThread]
+		static int Main(string[] args)
+		{
+			if (Debugger.IsAttached || args.Contains("--just-die"))
+				return (int)Game.InitializeAndRun(args);
+
+			AppDomain.CurrentDomain.UnhandledException += (_, e) => ExceptionHandler.HandleFatalError((Exception)e.ExceptionObject);
+
+			try
+			{
+				return (int)Game.InitializeAndRun(args);
+			}
+			catch (Exception e)
+			{
+				ExceptionHandler.HandleFatalError(e);
+				return (int)RunStatus.Error;
+			}
+		}
+	}
+}