mod: change interface for rendering of Layouts and Widgets to use a non-const pointer to the renderer instead

src/main.zig

@@ -26,7 +26,7 @@ pub fn main() !void {
     const allocator = gpa.allocator();
 
     var app: App = .{};
-    const renderer: App.Renderer = .{};
+    var renderer: App.Renderer = .{};
     // FIX: when not running fullscreen, the application needs to screen down accordingly to display the contents
     // -> size hint how much should it use?
 
@@ -142,6 +142,6 @@ pub fn main() !void {
         for (events.items) |e| {
             app.postEvent(e);
         }
-        try layout.render(renderer);
+        try layout.render(&renderer);
     }
 }