Split the Interface Building functionality into separate project/package.

[mohummedibrahim]

Hi @ChristianSauer, thanks for building this amazing source generator library.

I'm wondering if it would be possible to split the generator project and separate the interface-building functionality on its own? So the other source generators can also benefit from this.

I see there're a couple of issues with having the source generator depend on another library/project (e.g. dotnet/roslyn#47517 (comment))

If that's something you're willing to accept, please let me know, and I can create an initial PR.

Thanks again!

[ChristianSauer]

I am not opposed, but why want you do it? The interface building is really primitive, I've only used it because doing it right (i.e. building it by using the csharp compilationunit) is super annoying and too much for my use case.
What do you want to use it for?