## 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
from posthog.models.event.sql import EVENT_JOIN_PERSON_SQL
from posthog.models.filters import Filter, PathFilter
from posthog.models.filters.utils import validate_group_type_index
from posthog.models.property.util import get_property_string_expr
from posthog.models.team import Team
from posthog.queries.util import get_earliest_timestamp
logger = structlog.get_logger(__name__)
PROPERTY_MATH_FUNCTIONS = {
    "sum": "sum",
    "avg": "avg",
    "min": "min",
    "max": "max",
    "median": "quantile(0.50)",
    "p90": "quantile(0.90)",
    "p95": "quantile(0.95)",
    "p99": "quantile(0.99)",
}
COUNT_PER_ACTOR_MATH_FUNCTIONS = {
    "avg_count_per_actor": "avg",
    "min_count_per_actor": "min",
    "max_count_per_actor": "max",
    "median_count_per_actor": "quantile(0.50)",
    "p90_count_per_actor": "quantile(0.90)",
    "p95_count_per_actor": "quantile(0.95)",
    "p99_count_per_actor": "quantile(0.99)",
}
def process_math(
    entity: Entity, team: Team, event_table_alias: Optional[str] = None, person_id_alias: str = "person_id"
) -> Tuple[str, str, Dict[str, Any]]:
    aggregate_operation = "count(*)"