## Description

This PRs changes the default value transit mode for key event simulation.

The default transit mode for key event simulation is currently `KeyDataTransitMode.rawKeyData` while on the framework side `KeyDataTransitMode.keyDataThenRawKeyData` is the preferred transit mode.

`KeyDataTransitMode.keyDataThenRawKeyData` is more accurate and can help detect issues.

For instance the following test will fail with `KeyDataTransitMode.rawKeyData` because raw keyboard logic for modifier keys is less accurate:

```dart
  testWidgets('Press control left once', (WidgetTester tester) async {
    debugKeyEventSimulatorTransitModeOverride = KeyDataTransitMode.keyDataThenRawKeyData;

    final List<KeyEvent> events = <KeyEvent>[];
    final FocusNode focusNode = FocusNode();
    addTearDown(focusNode.dispose);

    await tester.pumpWidget(
      Focus(
        focusNode: focusNode,
        autofocus: true,
        onKeyEvent: (_, KeyEvent event) {
          events.add(event);
          return KeyEventResult.handled;
        },
        child: Container(),
      ),
    );

    await simulateKeyDownEvent(LogicalKeyboardKey.controlLeft);

    // This will fail when transit mode is KeyDataTransitMode.rawKeyData
    // because a down event for controlRight is synthesized.
    expect(events.length, 1);

    debugKeyEventSimulatorTransitModeOverride = null;
  });
```

And the following this test is ok with `KeyDataTransitMode.rawKeyData` but rightly fails with `KeyDataTransitMode.keyDataThenRawKeyData`:

```dart
  testWidgets('Simulates consecutive key down events', (WidgetTester tester) async {
    debugKeyEventSimulatorTransitModeOverride = KeyDataTransitMode.rawKeyData;

    // Simulating several key down events without key up in between is tolerated
    // when transit mode is KeyDataTransitMode.rawKeyData, it will trigger an
    // assert on KeyDataTransitMode.keyDataThenRawKeyData.
    await simulateKeyDownEvent(LogicalKeyboardKey.arrowDown);
    await simulateKeyDownEvent(LogicalKeyboardKey.arrowDown);

    debugKeyEventSimulatorTransitModeOverride = null;
  });
```

## Related Issue

Related to https://github.com/flutter/flutter/issues/143845

## Tests

Adds two tests.