Support deduplication of multi-value dimension for group by

[navis]

    testQuery(
        "SELECT bks_event_d0, count(*) as cnt FROM cdis GROUP BY bks_event_d0",
        new Object[]{"APP", 4L},
        new Object[]{"T114", 4L}
    );
    testQuery(
        "SELECT dedup(bks_event_d0), count(*) as cnt FROM cdis GROUP BY dedup(bks_event_d0)",
        new Object[]{"APP", 2L},
        new Object[]{"T114", 2L}
    );