Rename egui_demo to egui_demo_app to avoid confusion with egui_demo_lib

egui_demo_app/src/main.rs

@@ -0,0 +1,9 @@
+#![forbid(unsafe_code)]
+#![cfg_attr(not(debug_assertions), deny(warnings))] // Forbid warnings in release builds
+#![warn(clippy::all)]
+
+// When compiling natively:
+fn main() {
+    let app = egui_demo_lib::DemoApp::default();
+    eframe::run_native(Box::new(app));
+}