[NET10.0] Annotate ListStringTypeConverter for nullability

[MartyIX]

Description of Change

Recently, a PR was merged (#27984) where nullability annotations for ShadowTypeConverter were added. However, I believe that there are minor errors.

Based on dotnet/runtime#63874 which corrected nullable types for .NET runtime (e.g. DateTimeConverter), I believe that the correct method synopses are:

+public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
+public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destinationType)
+public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
+public override object? ConvertTo(ITypeDescriptorContext? context, CultureInfo? culture, object? value, Type destinationType)

This PR attempts to fix the annotations for a single converter to validate my beliefs.

---

If you wonder, what "~" character (called oblivious marker) denotes in PublicAPI.Shipped.txt and PublicAPI.Unshipped.txt files mean, then look here: https://github.com/dotnet/roslyn-analyzers/blob/main/src/PublicApiAnalyzers/PublicApiAnalyzers.Help.md#nullable-reference-type-support

Any public API that haven't been annotated (i.e. uses an oblivious reference type) will be tracked with a ~ marker.
The marker lets you track how many public APIs still lack annotations. For instance, ~C.ObliviousMethod() -> string.

[dotnet-policy-service]

Hey there @MartyIX! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[rmarinho]

I think the publicAPI changes are wrong, you need to add [Remove] tag on unshipped , the Shipped should not be changed..

[MartyIX]

I think the publicAPI changes are wrong, you need to add [Remove] tag on unshipped , the Shipped should not be changed..

Hopefully, it's correct now.

[rmarinho]

/Users/builder/azdo/_work/1/s/src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt(197,1): error RS0050: Symbol '~override Microsoft.Maui.Controls.ListStringTypeConverter.CanConvertFrom(System.ComponentModel.ITypeDescriptorContext context, System.Type sourceType) -> bool' is marked as removed but it isn't deleted in source code (https://github.com/dotnet/roslyn-analyzers/blob/main/src/PublicApiAnalyzers/PublicApiAnalyzers.Help.md) [/Users/builder/azdo/_work/1/s/src/Controls/src/Core/Controls.Core.csproj::TargetFramework=net10.0-android35.0]
/Users/builder/azdo/_work/1/s/src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt(198,1): error RS0050: Symbol '~override Microsoft.Maui.Controls.ListStringTypeConverter.CanConvertTo(System.ComponentModel.ITypeDescriptorContext context, System.Type destinationType) -> bool' is marked as removed but it isn't deleted in source code (https://github.com/dotnet/roslyn-analyzers/blob/main/src/PublicApiAnalyzers/PublicApiAnalyzers.Help.md) [/Users/builder/azdo/_work/1/s/src/Controls/src/Core/Controls.Core.csproj::TargetFramework=net10.0-android35.0]
/Users/builder/azdo/_work/1/s/src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt(199,1): error RS0050: Symbol '~override Microsoft.Maui.Controls.ListStringTypeConverter.ConvertFrom(System.ComponentModel.ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value) -> object' is marked as removed but it isn't deleted in source code (https://github.com/dotnet/roslyn-analyzers/blob/main/src/PublicApiAnalyzers/PublicApiAnalyzers.Help.md) [/Users/builder/azdo/_work/1/s/src/Controls/src/Core/Controls.Core.csproj::TargetFramework=net10.0-android35.0]
/Users/builder/azdo/_work/1/s/src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt(200,1): error RS0050: Symbol '~override Microsoft.Maui.Controls.ListStringTypeConverter.ConvertTo(System.ComponentModel.ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, System.Type destinationType) -> object' is marked as removed but it isn't deleted in source code (https://github.com/dotnet/roslyn-analyzers/blob/main/src/PublicApiAnalyzers/PublicApiAnalyzers.Help.md) [/Users/builder/azdo/_work/1/s/src/Controls/src/Core/Controls.Core.csproj::TargetFramework=net10.0-android35.0]
    1 Warning(s)
    24 Error(s)

Seems something is wrong, you can test locally first see if dotnet cake --workloads=global works