[Navigation] Why DataContext is being set only after control is loaded but not right after creation?

[xperiandri]

It creates a lot of issues:

1. Parrent DataContext is being propagated
   a. First null comes as DataContext
   b. Then parent view model comes as DataContext
   c. Only then right view model comes
2. CollectionViewSource created in XAML is not initialized and does not work

If you try my https://github.com/Ecierge/Elmish.Uno/tree/eCierge/src/Samples OneWaySeqGrouped page
Pay attention, branch eCierge
You will see that CollectionViewSource declared in XAML works.
But with Uno Navigation it does not

Are there any solutions for that?