This change fixes the problem when header would update to the previous screen configuration as a result of starting swipe back gesture but never restore to the original one in case swipe back gets cancelled (e.g. user didn't swipe far enough). The problem was that as a result of swipe back we'd apply header config changes but after cancel there was no trigger to reset header to the previous state.
On iOS by default modals show up in full-screen mode. This behavior can be customized and instead of mouting new screens in top level window they can be mounted under a given UINavController. We used to be relying on that behavior (see "CurrentContext" presentation mode). This, apparently wasn't matching the default functionality of the OS. This change is adding it as a default and keeping the old way under newly exposed presentation modes: containedModal and containedTransparentModal
Thanks to this change, iOS 13 modals can work properly.
