[Enhancement] New window with NavigationPage support

[JohnH-FF]

Summary

XF doesn't natively support multiple windows, make it so number 1!
Currently have to drop into platform specific code (via DI) to implement this, and provides a sub optimal solution.

API Changes

INavigation.PushToNewWindowAsync(Page page);

Intended Use Case

On desktop platforms this will push the page (or NavigationPage) into a new window. On mobile it will perform the same as INavigation.PushAsync until such time that mobile supports multi window (if ever).

[freever]

On mobile this could push to a modal dialog...?

[JohnH-FF]

@freever I was thinking that before I posted, but the better minds than mine at MS could decide if that workflow works. :)

[GalaxiaGuy]

Perhaps there should be an options parameter that could include PreferNewWindow leaving it up to the platform to handle? It could even replace the bool animated parameter:

[Flags]
public enum NavigationOptions
{
    None = 0,
    Animated = 1,
    PreferNewWindow = 2,
}