Make picocli-groovy an explicitly declared named JPMS module

[remkop]

Make picocli-groovy a named JPMS module with the following module-info:

/**
 * Defines API and implementation for building command line (CLI) applications with Groovy scripts.
 *
 * @since 4.7.0
 */
module info.picocli.groovy {
    requires info.picocli;
    requires groovy.all;

    exports picocli.groovy;
}

See also #1298