.NET MAUI 9: Markup extensions and extended type converters need `[RequiresService(typeof(T))]` or `[AcceptEmptyServiceProvider]` annotations

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In .NET MAUI 9, we now require all classes implementing IMarkupExtension, IMarkupExtension<T>, IValueProvider, and IExtendedTypeConverter to be annotated with either [RequireService(typeof(T))] or [AcceptEmptyServiceProvider] attributes. This was introduced in https://github.com/dotnet/maui/pull/19945.

For markup extensions, I think we need to update the examples and the "Service providers" section of Create XAML markup extensions
I currently don't know where the changes related to IValueProvider should go

In a migration guide or release notes, we should tell customers how to address warnings they might see, such as in the case of https://github.com/dotnet/maui/issues/24736:

XamlC warning XC0103: Consider attributing the markup extension "CommunityToolkit.Maui.Converters.IsNullConverter" with [RequireService] or [AcceptEmptyServiceProvider] if it doesn't require any.

Describe the change

We introduced a new optimization to XamlC which allows us to generate more efficient code when compiling XAML. This optimization helps reduce the final app size and also improve runtime performance.

Create XAML markup extensions

The example should be updated:

+[AcceptEmptyServiceProvider]
 public class HslColorExtension : IMarkupExtension<Color>
 {

The "Service providers" section

We should add a new paragraph describing the change:

for each use of serviceProvider.GetService(typeof(T)) in the ProvideValue method, the class should be annotated with [RequireService(typeof(T))] (Microsoft.Maui.Controls.Xaml.RequireServiceAttribute) such as for example here: https://github.com/dotnet/maui/blob/68b953b2ba020766ce8403455da209a12cf43564/src/Controls/src/Xaml/MarkupExtensions/ReferenceExtension.cs#L8-L40. It might be a good idea to show a more complete example of the usage of IProvideValueTarget with the attribute applied to the class.
if the markup extension doesn't use any service from the service provider, the class should be attributed with [AcceptEmptyServiceProvider] (Microsoft.Maui.Controls.Xaml.AcceptEmptyServiceProviderAttribute)

/cc @StephaneDelcroix @davidbritch

Associated WorkItem - 314394

dotnet / docs-maui