improve get_account_playlists perf

[stereosteve]

• move all filtering to CTE
• add where p.is_delete = false to final playlist select to ensure saves of deleted playlists get filtered out correctly? Unless we need delete for the tombstones.
• remove is_current filters... it does no filtering so can only hurt perf.
• add second sort... this is mostly for tests where all rows get created with the same timestamp... this makes the asserts more deterministic there.

CTE often can be optimization boundaries for the query planner... I'm surprised the before plan was so much worse (100x cost estimate).

Before:

 Gather Merge  (cost=203776.94..213213.83 rows=80882 width=50)
   Workers Planned: 2
   ->  Sort  (cost=202776.92..202878.02 rows=40441 width=50)
         Sort Key: p.created_at DESC
         ->  Nested Loop  (cost=176.66..199682.47 rows=40441 width=50)
               ->  Parallel Seq Scan on playlists p  (cost=176.23..34068.44 rows=40441 width=38)
                     Filter: (is_current AND (NOT is_delete) AND ((playlist_owner_id = 1) OR (hashed SubPlan 1)))
                     SubPlan 1
                       ->  Bitmap Heap Scan on saves  (cost=9.32..176.13 rows=41 width=4)
                             Recheck Cond: (((user_id = 1) AND (save_type = 'playlist'::savetype)) OR ((user_id = 1) AND (save_type = 'album'::savetype)))
                             Filter: (is_current AND (NOT is_delete))
                             ->  BitmapOr  (cost=9.32..9.32 rows=42 width=0)
                                   ->  Bitmap Index Scan on saves_new_user_id_save_type_idx  (cost=0.00..4.85 rows=42 width=0)
                                         Index Cond: ((user_id = 1) AND (save_type = 'playlist'::savetype))
                                   ->  Bitmap Index Scan on saves_new_user_id_save_type_idx  (cost=0.00..4.44 rows=1 width=0)
                                         Index Cond: ((user_id = 1) AND (save_type = 'album'::savetype))
               ->  Index Scan using idx_user_status on users u  (cost=0.43..4.09 rows=1 width=16)
                     Index Cond: (user_id = p.playlist_owner_id)
(18 rows)

After:

 Sort  (cost=2000.34..2000.62 rows=112 width=50)
   Sort Key: p.created_at DESC
   ->  Nested Loop  (cost=542.09..1996.52 rows=112 width=50)
         ->  Nested Loop  (cost=541.66..1609.96 rows=112 width=38)
               ->  HashAggregate  (cost=541.24..542.56 rows=132 width=4)
                     Group Key: saves.save_item_id
                     ->  Append  (cost=9.32..540.91 rows=132 width=4)
                           ->  Bitmap Heap Scan on saves  (cost=9.32..176.13 rows=41 width=4)
                                 Recheck Cond: (((user_id = 1) AND (save_type = 'playlist'::savetype)) OR ((user_id = 1) AND (save_type = 'album'::savetype)))
                                 Filter: (NOT is_delete)
                                 ->  BitmapOr  (cost=9.32..9.32 rows=42 width=0)
                                       ->  Bitmap Index Scan on saves_new_user_id_save_type_idx  (cost=0.00..4.85 rows=42 width=0)
                                             Index Cond: ((user_id = 1) AND (save_type = 'playlist'::savetype))
                                       ->  Bitmap Index Scan on saves_new_user_id_save_type_idx  (cost=0.00..4.44 rows=1 width=0)
                                             Index Cond: ((user_id = 1) AND (save_type = 'album'::savetype))
                           ->  Index Scan using playlist_owner_id_idx on playlists p_1  (cost=0.42..362.80 rows=91 width=4)
                                 Index Cond: (playlist_owner_id = 1)
                                 Filter: (NOT is_delete)
               ->  Index Scan using idx_playlist_status on playlists p  (cost=0.42..8.08 rows=1 width=38)
                     Index Cond: ((playlist_id = saves.save_item_id) AND (is_delete = false))
         ->  Index Scan using idx_user_status on users u  (cost=0.43..3.44 rows=1 width=16)
               Index Cond: (user_id = p.playlist_owner_id)