Previously when transparent card was requested we'd default to transparentModal stack presentation mode. However if user requests contained modal mode we should be using containedTransparentModal instead. This change fixes that behavior.
Appear event is used by react-navigation to properly dispatch focus. It is important that appear is dispatched after dismissed event. The reverse order of actions would result in getting react-navigation stack in a weird state.
It is relatively streightforward to implement onAppear event on iOS where we hook into didAppear callback from UIViewController. It gets dispatched in the right moment, that is when the transition is fully over.
On Android however it is much more tricky. There is no standard way to be notified from the fragment level that fragment transition finished. One way that is frequently recommended is to override Fragment.onCreateAnimation. However, this only works when custom transitions are provided (e.g. if we set the transition to use fade animation). As we want the platform native transition to be run by default we had to look for other ways. The current approach relies on fragment container's callbacks startViewTransition and endViewTransition, with the latter being triggered once the animation is over. We also need to take into account that a good starting point for the transition is when we call commit on fragment transaction. We use these two methods to determine if the fragment is instantiated (onCreate) within a running transaction and if so we schedule event dispatch at the moment when endViewTransition is called.
Another change this commit introduces on the Android side is that we no longer rely on show/hide for replacing fragments on stack and we now use add/remove transaction methods. Due to this change we had to make our fragments reusable and make onCreateView indempotent.
