[FEATURE] Add XmlnsDefinition

[dansiegel]

Is your feature request related to a problem? Please describe.

I'm a lazy programmer

Describe the solution you'd like

Add a XmlnsDefinitionAttribute so that it is easier to import anything we will need in XAML like:

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:skia="http://schemas.mono-project.com/skiasharp/2022/maui">
  <VerticalStackLayout>
    <skia:SkLottieView />
  </VerticalStackLayout>
</ContentPage>      

Describe alternatives you've considered

Not being lazy... but years of experience are working against me

Additional context

Because of a known issue with XamlC you need a hack to keep the assembly from getting linked out before XamlC can process the code. Or we'll need to finally get that bug fixed 😆