Simplify Iris app initialization and task updates

examples/minimal/desktop.rs

@@ -2,20 +2,7 @@ use iris::prelude::*;
 
 #[path = "lib.rs"]
 mod app;
-use app::*;
-
-#[derive(DesktopUiState)]
-struct State {
-    ui_state: DesktopUiState,
-}
-
-impl DesktopAppState for State {
-    fn new(mut ui_state: DesktopUiState, rsc: &mut StdRsc<Self>, _: Proxy<Self::Event>) -> Self {
-        build(rsc, &mut ui_state);
-        Self { ui_state }
-    }
-}
 
 fn main() {
-    DesktopApp::<State>::run();
+    DesktopApp::<DesktopUiState>::run_with(|ui_state, rsc| app::build(rsc, ui_state));
 }