Vert.x Code Generator breaks Java compilation with Gradle v4.7 annotationProcessor

I have reason to believe that the Vert.x Code Generator APT processor completely breaks Java compilation in Gradle when using with Gradle v4.7 and the `annotationProcessor`.

Found in https://github.com/vorburger/minecraft-storeys-maker/issues/53, but now reproduced in https://github.com/vorburger/vertx-gradle-errorprone-bug-reproducer. That very simple project fails when using `annotationProcessor` (but works when using `compile`). But an APT processor on `compile` instead of `annotationProcessor` breaks Error Prone. It's also "not right", and AFAIK doesn't play nice with Gradle's incremental build.

In an ideal world, Vert.x's Code Generator should "just work" (out of the box) with Gradle v4.7 annotationProcessor.

* https://docs.gradle.org/4.7/release-notes.html
* https://docs.gradle.org/4.6/release-notes.html#convenient-declaration-of-annotation-processor-dependencies