[Feature Request] Support C# Extension Syntax

[BlankDev117]

Is your feature request related to a problem? Please describe.
Yes, there is an issue with being able to use the new C# extensions:

public static class MyExtension 
{
    extension (IServiceCollection services)
    {
         public Result DoSomeCoolExtensionThing() 
         {
                .....
         }
    } 
}

I've seen errors relating to the following when attempting to run run: docfx docfx.json in CI/CD style pipelines in Github Actions:
error CS1520: Method must have a return type
error CS0710: Static classes cannot have instance constructors
error CS0708: '{memberName}': cannot declare instance members in a static class

Describe the solution you'd like
The new C# language features for extensions should not bork builds

Describe alternatives you've considered
Using standard extension with the older language features. This will work, but it's not staying modern.

Additional context
N/A

Note: If this is user error or something else I'm unaware of, let me know. Happy to close the issue due to ignorance on my part.