## 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)`.

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posthog/queries/trends/util.py
import datetime
from datetime import timedelta
from math import isinf, isnan
from typing import Any, Dict, List, Optional, Tuple, Union
import structlog
from rest_framework.exceptions import ValidationError
from sentry_sdk import capture_exception, push_scope
from posthog.constants import UNIQUE_USERS, WEEKLY_ACTIVE
from posthog.models.entity import Entity