Shellview support

[vb2ae]

          Hi, Caliburn.Micro was using for my enterprise app in WPF so I'm using Caliburn.Micro.Maui for migration and with the setup it's works good. But I'm trying to do the ShellView like [the tutorial for WPF ](https://caliburnmicro.com/documentation/Tutorials/WPF/ShellView)  . However with Window it does not work and causes a bug. [Window](https://learn.microsoft.com/en-us/dotnet/maui/fundamentals/windows?view=net-maui-7.0) seems to work with C# code and with Xaml there is no example.

<?xml version="1.0" encoding="utf-8" ?>
<Window xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="Formation.Views.ShellView"
             Title="ShellView">

    <!--With WPF-->
    <!--<Grid>
        <ContentControl x:Name="ActiveItem" Margin="20"/>
    </Grid>-->

    <ContentPage x:Name="ActiveItem"></ContentPage>

</Window>

Do you know how to make it work with the ShellView or maybe it's not yet implemented for MAUI. Otherwise how to change view with another page?

Originally posted by @Ryovenly in #831 (comment)