fix!: Migrate from RawKeyEvent to KeyEvent (#3002)

First pass at migrating from `RawKeyEvent` and `RawKeyboard`
to `KeyEvent` and `HardwareKeyboard`.

Context:
https://docs.flutter.dev/release/breaking-changes/key-event-migration

examples/lib/stories/system/without_flame_game_example.dart

@@ -30,10 +30,10 @@ class NoFlameGameExample extends Game with KeyboardEvents {
 
   @override
   KeyEventResult onKeyEvent(
-    RawKeyEvent event,
+    KeyEvent event,
     Set<LogicalKeyboardKey> keysPressed,
   ) {
-    final isKeyDown = event is RawKeyDownEvent;
+    final isKeyDown = event is KeyDownEvent;
 
     if (event.logicalKey == LogicalKeyboardKey.keyA) {
       velocity.x = isKeyDown ? -1 : 0;