Fix iOS compilation of eframe (emilk#4851)

Fixed changed the name of function `WinitApp::get_window_winit_id` to
`WinitApp::window_id_from_viewport_id` and missed `egui::ViewportId`
import.

Author: ardocrat

crates/eframe/src/native/run.rs

@@ -177,7 +177,7 @@ impl<T: WinitApp> WinitAppWrapper<T> {
             // WaitUntil seems to not work on iOS
             #[cfg(target_os = "ios")]
             winit_app
-                .get_window_winit_id(ViewportId::ROOT)
+                .window_id_from_viewport_id(egui::ViewportId::ROOT)
                 .map(|window_id| {
                     winit_app
                         .window(window_id)