ZomboDB requires AnyElement to retain an embedded OID

[workingjubilee]

This operator is a fundamental comparator in ZomboDB:

#[pg_extern(immutable, parallel_safe)]
fn anyelement_cmpfunc(
    element: AnyElement,
    query: ZDBQuery,
    fcinfo: pg_sys::FunctionCallInfo,
) -> bool {
    let (query_desc, query_state) = match get_executor_manager().peek_query_state() {
        Some((query_desc, query_state)) => (query_desc, query_state),
        None => return false,
    };
    let index_oid = match query_state.lookup_index_for_first_field(*query_desc, fcinfo) {
        Some(oid) => oid,
        None => return false,
    };

    let tid = if element.oid() == pg_sys::TIDOID {
        // use the ItemPointerData passed into us as the first argument
        Some(item_pointer_to_u64(
            unsafe { pg_sys::ItemPointerData::from_datum(element.datum(), element.oid()) }
                .unwrap(),
        ))
    } else {
        panic!(
            "The '==>' operator could not find a \"USING zombodb\" index that matches the left-hand-side of the expression"
        );
    };

    match tid {
        Some(tid) => unsafe {
            pg_func_extra(fcinfo, || do_seqscan(query, index_oid)).contains(&tid)
        },
        None => false,
    }
}

This was broken by #532.

[workingjubilee]

This was fixed by #615 being merged.