Ship V2 as a source generator instead of a library

[Blackclaws]

Adding libraries to source generators as dependencies is notoriously hard:

https://github.com/dotnet/roslyn/blob/main/docs/features/source-generators.cookbook.md#use-functionality-from-nuget-packages

And it gets worse if multiple generators use the same library but in different versions as roslyn does not currently load them into different domains.

Instead I would suggest shipping V2 as a generator in its own right that simply adds these files post initialization so they are compiled into the source generator directly without people needing to copy things manually.