BCV Gradle Plugin should not depend on kotlin-compiler-embeddable about binary-compatibility-validator

[JakeWharton]

1. Split the BCV generator and validator code into a separate subproject, which (just for quick reference) I'll call bcv-core.

2. bcv-core has an implementation dependency on kotlin-compiler-embeddable.

3. bcv-gradle (the current project has a whole) has a compileOnly dependency on bcv-core.

4. bcv-gradle uses the Worker API to invoke bcv-core using an isolated classpath.

5. BCV Gradle Plugin creates a Configuration for fetching bcv-core at runtime, and passing it into the Worker.

I also do 1 & 2 for all my tooling, but I differ on the rest. I tend to include a main() in what you call 'bcv-core', and then use the worker API + a dedicated configuration to javaexec that artifact. This avoids the compileOnly dependency and accidental references in the non-worker types, while also forcing you to provide the entrypoint for other build systems (but absolving you from actually having to do any additional work to integrate them).

(You could just use a JavaExec task as the configuration gives you isolation, but the worker API is the only way to enable project-local parallelism)