Update to .net maui

[VladislavAntonyuk]

Update to .NET MAUI

• Change target framework to net6.0
• Remove Xamarin Forms dependencies. Replace them with .NET MAUI (Update xaml, update some code (Color -> Colors, etc)
• Update namespaces (Xamarin.Forms -> Microsoft.Maui)
• Run Unit tests
• Pipeline fix

dotnet test is temporarily broken (the fix is already merged. waiting for a new build)

[jonathanpeppers]

So if Xamarin.Forms.Mocks were to support Maui, I would maybe do it in a new project, new NuGet package. Maui.Mocks?

Should we also investigate if this just needs to go in dotnet/maui itself?

Next time file an issue, and we can discuss before you do the work, thanks!

[stephanpalmer]

In our Xamarin.Forms apps, we extensively use Xamarin.Forms.Mocks to write acceptance and integration tests based on Xamarin.Forms.QuickTest. Basically we instantiate the complete platform-independent part of the Xamarin.Forms app in a unit testing project.

@jonathanpeppers We plan on doing the same with dotnet/maui once we migrate our apps. For this, it would be great if the possibility to instantiate all platform-independent classes was built in dotnet/maui itself, without the need for the workaround of an additional library.