Use horizonal sliding animations

[mars885]

For the horizontal sliding animations to work properly, they require specifying the zIndex for both the entering & exiting animations.

However, from the research done, it seems like it's not possible to specify it inside AnimatedNavHost.enterTransition, AnimatedNavHost.exitTransition, AnimatedNavHost.popEnterTransition, and AnimatedNavHost.popExitTransition as of 0.23.1 version of the Accompanist library.

The Accompanist's issue can be tracked here.