Fix phantom key presses in winit on focus change (#13299)

crates/bevy_winit/src/state.rs

@@ -223,16 +223,27 @@ impl<T: Event> ApplicationHandler<T> for WinitAppRunnerState<T> {
                 );
             }
             WindowEvent::CloseRequested => self.winit_events.send(WindowCloseRequested { window }),
-            WindowEvent::KeyboardInput { ref event, .. } => {
-                if event.state.is_pressed() {
-                    if let Some(char) = &event.text {
-                        let char = char.clone();
-                        #[allow(deprecated)]
-                        self.winit_events.send(ReceivedCharacter { window, char });
+            WindowEvent::KeyboardInput {
+                ref event,
+                is_synthetic,
+                ..
+            } => {
+                // Winit sends "synthetic" key press events when the window gains focus. These
+                // should not be handled, so we only process key events if they are not synthetic
+                // key presses. "synthetic" key release events should still be handled though, for
+                // properly releasing keys when the window loses focus.
+                if !(is_synthetic && event.state.is_pressed()) {
+                    // Process the keyboard input event, as long as it's not a synthetic key press.
+                    if event.state.is_pressed() {
+                        if let Some(char) = &event.text {
+                            let char = char.clone();
+                            #[allow(deprecated)]
+                            self.winit_events.send(ReceivedCharacter { window, char });
+                        }
                     }
+                    self.winit_events
+                        .send(converters::convert_keyboard_input(event, window));
                 }
-                self.winit_events
-                    .send(converters::convert_keyboard_input(event, window));
             }
             WindowEvent::CursorMoved { position, .. } => {
                 let physical_position = DVec2::new(position.x, position.y);