Using filter + within group is not supported

[crisptrutski]

Here is a minimally reproducing query:

  select
    e.instance_id
   -- this next one is fine
    , percentile_cont(0.75) within group (order by e.running_time) / 1000.0 as p75_time
   -- this is also fine
    , avg(e.running_time) filter (where e.error = '') / 1000.0 as avg_success_time
   -- this one causes a parse error
    , percentile_cont(0.75) within group (order by e.running_time) filter (where e.error = '') / 1000.0 as p75_success_time
  from execution e
  group by 1