implement launch builder for the desktop and web platforms

examples/filedragdrop.rs

@@ -2,18 +2,16 @@ use dioxus::prelude::*;
 use dioxus_desktop::Config;
 
 fn main() {
-    Config::new()
-        .with_file_drop_handler(|_w, e| {
+    LaunchBuilder::new(app)
+        .cfg(Config::new().with_file_drop_handler(|_w, e| {
             println!("{e:?}");
             true
-        })
-        .launch(app)
+        }))
+        .launch()
 }
 
 fn app() -> Element {
     rsx!(
-        div {
-            h1 { "drag a file here and check your console" }
-        }
+        div { h1 { "drag a file here and check your console" } }
     )
 }