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/custom_font/src/main.rs

@@ -2,7 +2,7 @@
 
 use eframe::egui;
 
-fn main() {
+fn main() -> Result<(), eframe::EframeError> {
     let options = eframe::NativeOptions {
         initial_window_size: Some(egui::vec2(320.0, 240.0)),
         ..Default::default()
@@ -11,7 +11,7 @@ fn main() {
         "egui example: custom font",
         options,
         Box::new(|cc| Box::new(MyApp::new(cc))),
-    );
+    )
 }
 
 fn setup_custom_fonts(ctx: &egui::Context) {