implement launch builder for the desktop and web platforms

examples/router.rs

@@ -5,7 +5,7 @@ fn main() {
     #[cfg(target_arch = "wasm32")]
     dioxus_web::launch(App);
     #[cfg(not(target_arch = "wasm32"))]
-    dioxus_desktop::launch(App);
+    launch(App);
 }
 
 // ANCHOR: router