Could PostGraphile use (more) CTEs/JOINs instead of subqueries?

For a GraphQL query such as:

```graphql
{
objects {
id
states {
someField
# ... more fields here ...
}
}
}
```

PostGraphile generates the following SQL:

```sql
select
__objects__."id"::text as "0",
array(
select array[
__object_states__."some_field"::text,
-- ... more fields here ...
]::text[]
from "postgraphile_schema"."object_states" as __object_states__
where (
__object_states__."object_id" = __objects__."id"
)
order by __object_states__."id" asc
)::text as "1"
from "postgraphile_schema"."objects" as __objects__
order by __objects__."id" asc;
```

This is slow, because `"postgraphile_schema"."object_states"` is an expensive-to-compute view, and because it is in a subquery, it is recomputed for every row in `__objects__`.

The following equivalent query is much faster:

```sql
with __object_states__ as (
select *
from "postgraphile_schema"."object_states"
)
select
__objects__.id::text as "0",
array_agg(
array[
__object_states__."some_field"::text,
-- ... more fields here ...
]::text[]
order by __object_states__.id asc
)::text as "1"
from "postgraphile_schema"."objects" as __objects__
left join __object_states__ on __objects__.id = __object_states__.object_id
group by __objects__.id
order by __objects__.id asc;
```

Could PostGraphile generate SQL code closer to the second variant?