iOS 14 navigation workaround

[carmelogallo]

In iOS 14 the .fullScreenCover and .sheet modifier can't be more than one per view so we use the workaround found on this thread.

case .fullscreen:
    // In iOS 14 the .fullScreenCover modifier can't be more than one per view
    // so we use the workaround found on this thread.
    // https://stackoverflow.com/a/64403206/2242854
    if #available(iOS 15, *) {
        content.fullScreenCover(isPresented: $state.isPresented) { LazyView(navigationContent()) }
    } else {
        Group {
            EmptyView().fullScreenCover(isPresented: $state.isPresented) { LazyView(navigationContent()) }
            content
        }
    }
case .sheet:
    // In iOS 14 the .sheet modifier can't be more than one per view
    // so we use the workaround found on this thread.
    // https://stackoverflow.com/a/64403206/2242854
    if #available(iOS 15, *) {
        content.sheet(isPresented: $state.isPresented) { LazyView(navigationContent()) }
    } else {
        Group {
            EmptyView().sheet(isPresented: $state.isPresented) { LazyView(navigationContent()) }
            content
        }
    }