Navigation transitions: default to the platform

Every Frame.navigate() (and RouterExtensions.navigate() in Angular) accepts a transition option. The correct value, almost always, is none at all. Omit it and NativeScript hands the navigation to the OS — UINavigationController's push/pop on iOS, the native fragment transition (with predictive back) on Android.

// WRONG: downgrades the experience — looks close to native, feels wrong
frame.navigate({
  moduleName: 'views/item/item-page',
  context: { id: item.id },
  transition: { name: 'slideLeft' },
});

// RIGHT: platform-default animation
frame.navigate({
  moduleName: 'views/item/item-page',
  context: { id: item.id },
});