Add custom screen presentation styles

[ohitsdaniel]

Idea

Currently, we only support two screen presentation styles: push and sheet. We could add a way to define custom screen presentation styles.

Problem description

Custom screen presentation styles are a bit tricky as they involve local state for animation. SwiftUI defines animations on a view basis and we could come up with something along the lines of

protocol ScreenTransition: Hashable {
  func animatedContent<Content: View>(content: Content, isVisible: Bool) -> some View
}

struct FullScreenCoverTransition: ScreenTransition {
   func animatedContent<Content: View>(content: Content, isVisible: Bool) -> some View {
    content
      .animationModifiers() // do whatever you want here 
  }
}

We would then need to plug this into NavigationNode and make sure that we properly perform the animation on show and dismiss.