## Bug description

When calculating Trends results with an aggregated (e.g. single output, like big number) display type, WAU/MAU don't work. This is because we have an `ACTIVE_USERS_SQL` query for time series display types, but we don't have a version of this for aggregated display types. (See ZEN-1043.)

## How to reproduce

1. Create an insight with a single WAU or MAU series.
2. Switch display type to "Number".
3. Open the "Debug ClickHouse queries" modal from the command palette.
4. See `COUNT(*)` instead of `COUNT(DISTINCT person_id)`.

#### *Thank you* for your bug report – we love squashing them!

posthog/queries/breakdown_props.py
breakdown_type: Optional[BREAKDOWN_TYPES],
    breakdown: Union[str, List[Union[str, int]], None],
    breakdown_group_type_index: Optional[GroupTypeIndex],
    breakdown_normalize_url: bool = False,
    direct_on_events: bool = False,
    cast_as_float: bool = False,
) -> str:
    if breakdown_type == "session":
        if breakdown == "$session_duration":
            
            
            value_expression = f"{SessionQuery.SESSION_TABLE_ALIAS}.session_duration"
        else:
            raise ValidationError(f'Invalid breakdown "{breakdown}" for breakdown type "session"')
    elif breakdown_type == "person":
        value_expression = get_single_or_multi_property_string_expr(
            breakdown,
            query_alias=None,
            table="events" if direct_on_events else "person",
            column="person_properties" if direct_on_events else "person_props",
            allow_denormalized_props=True,
            materialised_table_column="person_properties" if direct_on_events else "properties",
        )