Moves viewControllerForKey to use viewForKey with transitions where appropriate as discussed in this Stack Overflow post: https://stackoverflow.com/questions/24338700/from-view-controller-disappears-using-uiviewcontrollercontexttransitioning/25193675#25193675

This mainly resolves an issue when using animations with `dismissModal` that results in all views being removed and a black screen appearing as discussed in #6195 

The remaining `viewControllerForKey` calls should probably be removed too where their `view` property is being used, but this seems to resolve the bug for now at least!