Make picocli-shell-jline2 an explicitly declared named JPMS module

Make picocli-shell-jline2 a named JPMS module with the following `module-info`:

```java
/**
 * Defines picocli-based implementations of JLine 2 APIs
 * for building interactive command line (REPL) applications.
 *
 * @since 4.7.0
 */
module info.picocli.shell.jline2 {
    requires info.picocli;
    requires jline;

    exports picocli.shell.jline2;
}
```

See also #1298