WindowServer: Replace window menu action magic numbers with enum

This makes it a lot easier to find where the action handling is
happening, just 1, 2, 3, 4 isn't very discoverable. :^)

Userland/Services/WindowServer/Window.h

@@ -71,6 +71,13 @@ enum class PopupMenuItem {
     Maximize,
 };
 
+enum class WindowMenuAction {
+    MinimizeOrUnminimize = 0,
+    MaximizeOrRestore,
+    ToggleMenubarVisibility,
+    Close,
+};
+
 enum class WindowMenuDefaultAction {
     None = 0,
     BasedOnWindowState,