Annotation processor should allow @Spec-annotated field in version provider

[remkop]

Picocli 4.2.0 added support for injecting CommandSpec into custom IVersionProvider implementation classes.

However, the annotation processor raises a compile-time error with message @Spec must be enclosed in a @Command, but was <class> when a IVersionProvider implementation class has a @Spec-annotated field.

(picocli-codegen/src/main/java/picocli/codegen/annotation/processing/AbstractCommandSpecProcessor.java, line 843).

The workaround is to use variables like ${COMMAND-NAME} or ${COMMAND-FULL-NAME} in the returned version string.