Embed GraphQL metadata in the jar/klib

[martinbonnin]

Use case

As of today, we use a separate file to store GraphQL metadata used by the apollo compiler. This means in multi-module scenarios, one typically has to do something like so:

dependencies {
  implementation(project(":schema"))
}

apollo {
  service("service") {
    dependsOn(project(":schema"))
  }
}

While working, this setup is a bit cumbersome and error prone. It's possible to forget one of the two dependencies.

Instead, we could embed the required GraphQL information in the .jar/.klib file so that the apollo compiler doesn't have to pull an additional artifact.

See #6325
See https://youtrack.jetbrains.com/issue/KT-58830

[martinbonnin]

Note: if we're going that road, we might not be able to share the same codegen task between different targets/variants anymore.

KMP has targets and Android have variants. Each target/variant has its own "compileClasspath" that may be different so we'd need to create N schema, Ir, codegen, etc... tasks. That's going to blow up the number of codegen tasks quite a lot. Maybe not an issue but it's added complexity.

Or maybe we can find a "common" "compileClasspath" that we could reuse. This will need to be user-configurable.