eframe error handling (#2433)

* eframe::run_native: return errors instead of crashing

* Detect and handle glutin errors

* egui_demo_app: silence wgpu log spam

* Add trace logs for why eframe is shutting down

* Fix: only save App state once on Mac

* Handle Winit failure

* Log where we load app state from

* Don't panic on zero-sized window

* Clamp loaded window size to not be too tiny to see

* Simplify code: more shared code in window_builder

* Improve code readability

* Fix wasm32 build

* fix android

* Update changelog

examples/retained_image/src/main.rs

@@ -3,7 +3,7 @@
 use eframe::egui;
 use egui_extras::RetainedImage;
 
-fn main() {
+fn main() -> Result<(), eframe::EframeError> {
     let options = eframe::NativeOptions {
         initial_window_size: Some(egui::vec2(300.0, 900.0)),
         ..Default::default()
@@ -13,7 +13,7 @@ fn main() {
         "Show an image with eframe/egui",
         options,
         Box::new(|_cc| Box::new(MyApp::default())),
-    );
+    )
 }
 
 struct MyApp {