Only regenerate Scala files from GraphQL schema if schema changes about sbt-graphql

[felixbr]

So, I've upgraded to 0.16.0 at work and it seems like the incremental compilation is working quite well there already.

My guess is that some of the codegen tasks where rearranged in a way that sbt understands and caches them automatically. From the docs:

sbt will automatically track the outputs of any task that returns one of the following result types: Path, Seq[Path], File or Seq[File].

https://www.scala-sbt.org/1.x/docs/Howto-Track-File-Inputs-and-Outputs.html

I'll see how it goes with the latest version and if everything's working as expected we can close this 🙂