Add an option to opt in to XAML C# Expressions in .NET MAUI 10+

[egvijayanand]

• Add an option to opt in to XAML C# Expressions in .NET MAUI 10+
• This will be an optional Boolean parameter
• -xce | --xaml-cs-expr - Default value is false
• Not applicable to earlier versions of .NET MAUI
• Works better with MVVM opt-in
• RelayCommand from the MVVM Toolkit does not apply, as it is decorated on the method, making the generated property invisible to the .NET MAUI Source Gen
• SourceGen option and Preview Features flag will be enabled implicitly

<Label
    FontAttributes="Bold"
    FontSize="18"
    HorizontalOptions="Center"
    Style="{StaticResource MauiLabel}"
    Text="{CountText}" />

dotnet new mauiapp -o MyApp -mvvm -xce