Add stats button to end game dialog

Also adds the statistics window to TD.  There is no button for it in
observer mode, though, but it is available from the end game dialog.

Fixes #6312.

OpenRA.Mods.RA/Widgets/Logic/Ingame/LeaveMapLogic.cs

@@ -29,10 +29,22 @@ namespace OpenRA.Mods.RA.Widgets
 			if (showObjectives)
 				panelName = "LEAVE_RESTART_FULL";
 
+			var showStats = false;
+
 			var dialog = widget.Get<ContainerWidget>(panelName);
-			dialog.IsVisible = () => true;
+			dialog.IsVisible = () => !showStats;
 			widget.IsVisible = () => Ui.CurrentWindow() == null;
 
+			var statsButton = dialog.Get<ButtonWidget>("STATS_BUTTON");
+			statsButton.OnClick = () =>
+			{
+				showStats = true;
+				Game.LoadWidget(world, "INGAME_OBSERVERSTATS_BG", Ui.Root, new WidgetArgs()
+				{
+					{ "onExit", () => showStats = false }
+				});
+			};
+
 			var leaveButton = dialog.Get<ButtonWidget>("LEAVE_BUTTON");
 			leaveButton.OnClick = () =>
 			{