egui_glium: run app code outside event loop to fix file dialogs (#631)

Previously app code was run from within the event loop
which lead to file dialogs (e.g. using nfd2) to hang
(see https://github.com/rust-windowing/winit/issues/1779)

Now egui_glium polls for events and then runs the app code.

eframe/CHANGELOG.md

@@ -4,6 +4,7 @@ All notable changes to the `eframe` crate.
 
 ## Unreleased
 * Improve http fetch API.
+* `run_native` now returns when the app is closed.
 
 
 ## 0.13.1 - 2021-06-24

eframe/src/lib.rs

@@ -68,6 +68,6 @@ pub fn start_web(canvas_id: &str, app: Box<dyn epi::App>) -> Result<(), wasm_bin
 
 /// Call from `fn main` like this: `eframe::run_native(Box::new(MyEguiApp::default()))`
 #[cfg(not(target_arch = "wasm32"))]
-pub fn run_native(app: Box<dyn epi::App>, native_options: epi::NativeOptions) -> ! {
+pub fn run_native(app: Box<dyn epi::App>, native_options: epi::NativeOptions) {
     egui_glium::run(app, native_options)
 }