chore: fix build failure issue when using c# 14 extension members

[filzrev]

This PR add limited support for C# 14 Extension members syntax.

Currently it throw exception when some C# features are used.
By this PR it can use C# 14 syntax without error.

What's changed in this PR

• Add code to handle TypeKind.Extension enum value.
• Add code to skip Extension Members symbol as temporary workaround for issue described below.
• Add C# 13/14 syntax test code under samples/csharp/src directory.

Background
When using C# extension members
INamedTypeSymbol is generated per extension blocks.
And following property is exposed.

• ExtensionGroupingName // e.g. <G>$8B58B811E742D8E9EA7E14F878F87B0F
• ExtensionMarkerName // e.g. <M>$2C37A6F24442AF359D03A7723186221C
• ExtensionParameter: // IParameterSymbol that specified at extension block.

These names are used for DocumentationCommentId also.
And it contains <, > chars so need to be escape when output YAML files.

Limitation

• Extension Members are not shown on target type's extension method/property.
• extension blocks are not shown on static class extensions.

[mikernet]

I tried building the docs for https://github.com/Singulink/Singulink.UI/ using this branch and it no longer throws an exception during doc build but it also doesn't show the extension members.

The generated docs: https://www.singulink.com/Docs/Singulink.UI/api/Singulink.UI.Navigation.ViewModelExtensions.html

The source file: https://github.com/Singulink/Singulink.UI/blob/main/Source/Singulink.UI.Navigation/ViewModelExtensions.cs

[mikernet]

I also tried it with the modern template just to make sure it wasn't something template related and it's not showing there either.

[filzrev]

I've renamed PR title.
As described at description. This PR intended to fix build failure issue when C# 14 syntax used.